Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $249.84   5.804%   $264.3407   $264.34   $264.35   $264.30  
  Purchase #2 $215.93   5.153%   $227.0569   $227.06   $227.05   $227.10  
  Purchase #3 $130.75   10.284%   $144.1963   $144.20   $144.20   $144.20  
  Purchase #4 $214.43   13.689%   $243.7833   $243.78   $243.80   $243.80  
  Purchase #5 $182.71   9.623%   $200.2922   $200.29   $200.30   $200.30  
  Purchase #6 $217.83   13.142%   $246.4572   $246.46   $246.45   $246.50  
  Purchase #7 $220.35   10.384%   $243.2311   $243.23   $243.25   $243.20  
  7 purchase totals = $1,431.84       $1,569.3577   $1,569.36   $1,569.40   $1,569.40