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 $193.32   11.117%   $214.8114   $214.81   $214.80   $214.80  
  Purchase #2 $161.94   7.654%   $174.3349   $174.33   $174.35   $174.30  
  Purchase #3 $159.67   6.462%   $169.9879   $169.99   $170.00   $170.00  
  Purchase #4 $169.86   13.676%   $193.0901   $193.09   $193.10   $193.10  
  Purchase #5 $93.90   3.542%   $97.2259   $97.23   $97.25   $97.20  
  Purchase #6 $148.72   11.870%   $166.3731   $166.37   $166.35   $166.40  
  Purchase #7 $32.75   13.218%   $37.0789   $37.08   $37.10   $37.10  
  7 purchase totals = $960.16       $1,052.9022   $1,052.90   $1,052.95   $1,052.90