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 $200.59   5.718%   $212.0597   $212.06   $212.05   $212.10  
  Purchase #2 $171.88   10.349%   $189.6679   $189.67   $189.65   $189.70  
  Purchase #3 $66.26   12.854%   $74.7771   $74.78   $74.80   $74.80  
  Purchase #4 $139.65   3.778%   $144.926   $144.93   $144.95   $144.90  
  Purchase #5 $211.78   5.142%   $222.6697   $222.67   $222.65   $222.70  
  Purchase #6 $212.58   11.641%   $237.3264   $237.33   $237.35   $237.30  
  Purchase #7 $175.73   5.300%   $185.0437   $185.04   $185.05   $185.00  
  7 purchase totals = $1,178.47       $1,266.4705   $1,266.48   $1,266.50   $1,266.50