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 $53.54   10.173%   $58.9866   $58.99   $59.00   $59.00  
  Purchase #2 $194.40   11.271%   $216.3108   $216.31   $216.30   $216.30  
  Purchase #3 $246.89   7.157%   $264.5599   $264.56   $264.55   $264.60  
  Purchase #4 $225.51   6.625%   $240.45   $240.45   $240.45   $240.50  
  Purchase #5 $44.53   13.289%   $50.4476   $50.45   $50.45   $50.40  
  Purchase #6 $243.43   9.626%   $266.8626   $266.86   $266.85   $266.90  
  Purchase #7 $122.79   12.484%   $138.1191   $138.12   $138.10   $138.10  
  7 purchase totals = $1,131.09       $1,235.7366   $1,235.74   $1,235.70   $1,235.80