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 $146.35   11.425%   $163.0705   $163.07   $163.05   $163.10  
  Purchase #2 $247.60   11.289%   $275.5516   $275.55   $275.55   $275.60  
  Purchase #3 $149.45   8.605%   $162.3102   $162.31   $162.30   $162.30  
  Purchase #4 $72.98   8.290%   $79.03   $79.03   $79.05   $79.00  
  Purchase #5 $27.65   13.554%   $31.3977   $31.40   $31.40   $31.40  
  Purchase #6 $237.50   6.701%   $253.4149   $253.41   $253.40   $253.40  
  Purchase #7 $37.82   5.172%   $39.7761   $39.78   $39.80   $39.80  
  7 purchase totals = $919.35       $1,004.5510   $1,004.55   $1,004.55   $1,004.60