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 $92.72   11.828%   $103.6869   $103.69   $103.70   $103.70  
  Purchase #2 $182.72   8.199%   $197.7012   $197.70   $197.70   $197.70  
  Purchase #3 $46.64   5.558%   $49.2323   $49.23   $49.25   $49.20  
  Purchase #4 $28.69   11.173%   $31.8955   $31.90   $31.90   $31.90  
  Purchase #5 $93.82   13.681%   $106.6555   $106.66   $106.65   $106.70  
  Purchase #6 $160.56   9.283%   $175.4648   $175.46   $175.45   $175.50  
  Purchase #7 $244.95   7.155%   $262.4762   $262.48   $262.50   $262.50  
  7 purchase totals = $850.10       $927.1124   $927.12   $927.15   $927.20