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 $204.56   13.394%   $231.9588   $231.96   $231.95   $232.00  
  Purchase #2 $84.54   10.267%   $93.2197   $93.22   $93.20   $93.20  
  Purchase #3 $216.36   13.425%   $245.4063   $245.41   $245.40   $245.40  
  Purchase #4 $67.29   9.596%   $73.7471   $73.75   $73.75   $73.70  
  Purchase #5 $222.60   8.277%   $241.0246   $241.02   $241.00   $241.00  
  Purchase #6 $100.85   12.405%   $113.3604   $113.36   $113.35   $113.40  
  Purchase #7 $247.25   8.432%   $268.0981   $268.10   $268.10   $268.10  
  7 purchase totals = $1,143.45       $1,266.8150   $1,266.82   $1,266.75   $1,266.80