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 $244.93   5.536%   $258.4893   $258.49   $258.50   $258.50  
  Purchase #2 $132.99   10.712%   $147.2359   $147.24   $147.25   $147.20  
  Purchase #3 $104.34   13.651%   $118.5835   $118.58   $118.60   $118.60  
  Purchase #4 $131.74   13.840%   $149.9728   $149.97   $149.95   $150.00  
  Purchase #5 $208.86   6.786%   $223.0332   $223.03   $223.05   $223.00  
  Purchase #6 $42.27   10.339%   $46.6403   $46.64   $46.65   $46.60  
  Purchase #7 $90.96   4.217%   $94.7958   $94.80   $94.80   $94.80  
  7 purchase totals = $956.09       $1,038.7508   $1,038.75   $1,038.80   $1,038.70