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 $237.55   11.544%   $264.9728   $264.97   $264.95   $265.00  
  Purchase #2 $88.41   12.738%   $99.6717   $99.67   $99.65   $99.70  
  Purchase #3 $102.34   11.377%   $113.9832   $113.98   $114.00   $114.00  
  Purchase #4 $38.95   8.775%   $42.3679   $42.37   $42.35   $42.40  
  Purchase #5 $144.93   11.799%   $162.0303   $162.03   $162.05   $162.00  
  Purchase #6 $217.56   7.697%   $234.3056   $234.31   $234.30   $234.30  
  Purchase #7 $52.82   10.426%   $58.327   $58.33   $58.35   $58.30  
  7 purchase totals = $882.56       $975.6585   $975.66   $975.65   $975.70