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 $116.94   12.825%   $131.9376   $131.94   $131.95   $131.90  
  Purchase #2 $147.65   3.249%   $152.4471   $152.45   $152.45   $152.40  
  Purchase #3 $44.99   13.266%   $50.9584   $50.96   $50.95   $51.00  
  Purchase #4 $179.59   5.701%   $189.8284   $189.83   $189.85   $189.80  
  Purchase #5 $195.99   5.773%   $207.3045   $207.30   $207.30   $207.30  
  Purchase #6 $5.40   8.443%   $5.8559   $5.86   $5.85   $5.90  
  Purchase #7 $21.52   13.525%   $24.4306   $24.43   $24.45   $24.40  
  7 purchase totals = $712.08       $762.7625   $762.77   $762.80   $762.70