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 $203.76   5.626%   $215.2235   $215.22   $215.20   $215.20  
  Purchase #2 $97.90   9.834%   $107.5275   $107.53   $107.55   $107.50  
  Purchase #3 $113.97   5.716%   $120.4845   $120.48   $120.50   $120.50  
  Purchase #4 $180.58   13.516%   $204.9872   $204.99   $205.00   $205.00  
  Purchase #5 $204.42   10.368%   $225.6143   $225.61   $225.60   $225.60  
  Purchase #6 $59.40   12.220%   $66.6587   $66.66   $66.65   $66.70  
  Purchase #7 $91.28   6.831%   $97.5153   $97.52   $97.50   $97.50  
  7 purchase totals = $951.31       $1,038.0110   $1,038.01   $1,038.00   $1,038.00