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 $167.97   13.304%   $190.3167   $190.32   $190.30   $190.30  
  Purchase #2 $212.79   3.470%   $220.1738   $220.17   $220.15   $220.20  
  Purchase #3 $68.39   7.326%   $73.4003   $73.40   $73.40   $73.40  
  Purchase #4 $185.84   5.126%   $195.3662   $195.37   $195.35   $195.40  
  Purchase #5 $167.62   3.766%   $173.9326   $173.93   $173.95   $173.90  
  Purchase #6 $67.89   10.145%   $74.7774   $74.78   $74.80   $74.80  
  Purchase #7 $23.60   11.599%   $26.3374   $26.34   $26.35   $26.30  
  7 purchase totals = $894.10       $954.3044   $954.31   $954.30   $954.30