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 $228.54   3.524%   $236.5937   $236.59   $236.60   $236.60  
  Purchase #2 $155.45   7.525%   $167.1476   $167.15   $167.15   $167.10  
  Purchase #3 $83.29   9.625%   $91.3067   $91.31   $91.30   $91.30  
  Purchase #4 $86.59   12.332%   $97.2683   $97.27   $97.25   $97.30  
  Purchase #5 $212.98   13.458%   $241.6428   $241.64   $241.65   $241.60  
  Purchase #6 $235.87   13.418%   $267.519   $267.52   $267.50   $267.50  
  Purchase #7 $248.35   6.750%   $265.1136   $265.11   $265.10   $265.10  
  7 purchase totals = $1,251.07       $1,366.5917   $1,366.59   $1,366.55   $1,366.50