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 $86.52   9.262%   $94.5335   $94.53   $94.55   $94.50  
  Purchase #2 $215.62   10.466%   $238.1868   $238.19   $238.20   $238.20  
  Purchase #3 $214.53   4.698%   $224.6086   $224.61   $224.60   $224.60  
  Purchase #4 $27.45   12.709%   $30.9386   $30.94   $30.95   $30.90  
  Purchase #5 $10.33   10.609%   $11.4259   $11.43   $11.45   $11.40  
  Purchase #6 $236.61   7.150%   $253.5276   $253.53   $253.55   $253.50  
  Purchase #7 $62.53   7.184%   $67.0222   $67.02   $67.00   $67.00  
  7 purchase totals = $853.59       $920.2432   $920.25   $920.30   $920.10