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 $76.38   11.761%   $85.3631   $85.36   $85.35   $85.40  
  Purchase #2 $136.94   6.313%   $145.585   $145.59   $145.60   $145.60  
  Purchase #3 $209.68   3.328%   $216.6582   $216.66   $216.65   $216.70  
  Purchase #4 $225.77   4.798%   $236.6024   $236.60   $236.60   $236.60  
  Purchase #5 $46.65   8.110%   $50.4333   $50.43   $50.45   $50.40  
  Purchase #6 $140.32   11.584%   $156.5747   $156.57   $156.55   $156.60  
  Purchase #7 $232.54   11.373%   $258.9868   $258.99   $259.00   $259.00  
  7 purchase totals = $1,068.28       $1,150.2035   $1,150.20   $1,150.20   $1,150.30