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 $29.28   5.149%   $30.7876   $30.79   $30.80   $30.80  
  Purchase #2 $83.52   12.761%   $94.178   $94.18   $94.20   $94.20  
  Purchase #3 $24.96   3.356%   $25.7977   $25.80   $25.80   $25.80  
  Purchase #4 $163.92   3.839%   $170.2129   $170.21   $170.20   $170.20  
  Purchase #5 $45.82   10.321%   $50.5491   $50.55   $50.55   $50.50  
  Purchase #6 $98.42   8.499%   $106.7847   $106.78   $106.80   $106.80  
  Purchase #7 $49.86   7.820%   $53.7591   $53.76   $53.75   $53.80  
  7 purchase totals = $495.78       $532.0691   $532.07   $532.10   $532.10