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 $233.94   11.586%   $261.0443   $261.04   $261.05   $261.00  
  Purchase #2 $60.32   7.178%   $64.6498   $64.65   $64.65   $64.60  
  Purchase #3 $50.98   10.281%   $56.2213   $56.22   $56.20   $56.20  
  Purchase #4 $170.59   4.383%   $178.067   $178.07   $178.05   $178.10  
  Purchase #5 $188.32   9.381%   $205.9863   $205.99   $206.00   $206.00  
  Purchase #6 $177.59   11.114%   $197.3274   $197.33   $197.35   $197.30  
  Purchase #7 $66.84   12.353%   $75.0967   $75.10   $75.10   $75.10  
  7 purchase totals = $948.58       $1,038.3928   $1,038.40   $1,038.40   $1,038.30