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 $60.86   12.416%   $68.4164   $68.42   $68.40   $68.40  
  Purchase #2 $221.95   5.106%   $233.2828   $233.28   $233.30   $233.30  
  Purchase #3 $210.35   7.690%   $226.5259   $226.53   $226.55   $226.50  
  Purchase #4 $226.95   11.179%   $252.3207   $252.32   $252.30   $252.30  
  Purchase #5 $161.47   9.510%   $176.8258   $176.83   $176.85   $176.80  
  Purchase #6 $46.52   9.303%   $50.8478   $50.85   $50.85   $50.80  
  Purchase #7 $199.86   10.179%   $220.2037   $220.20   $220.20   $220.20  
  7 purchase totals = $1,127.96       $1,228.4231   $1,228.43   $1,228.45   $1,228.30