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 $207.88   12.825%   $234.5406   $234.54   $234.55   $234.50  
  Purchase #2 $133.53   11.854%   $149.3586   $149.36   $149.35   $149.40  
  Purchase #3 $186.44   4.626%   $195.0647   $195.06   $195.05   $195.10  
  Purchase #4 $42.82   12.303%   $48.0881   $48.09   $48.10   $48.10  
  Purchase #5 $153.56   10.396%   $169.5241   $169.52   $169.50   $169.50  
  Purchase #6 $40.33   4.656%   $42.2078   $42.21   $42.20   $42.20  
  Purchase #7 $201.68   10.104%   $222.0577   $222.06   $222.05   $222.10  
  7 purchase totals = $966.24       $1,060.8416   $1,060.84   $1,060.80   $1,060.90