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 $40.66   6.766%   $43.4111   $43.41   $43.40   $43.40  
  Purchase #2 $84.98   8.514%   $92.2152   $92.22   $92.20   $92.20  
  Purchase #3 $177.35   13.779%   $201.7871   $201.79   $201.80   $201.80  
  Purchase #4 $222.88   8.480%   $241.7802   $241.78   $241.80   $241.80  
  Purchase #5 $210.68   9.210%   $230.0836   $230.08   $230.10   $230.10  
  Purchase #6 $47.65   12.137%   $53.4333   $53.43   $53.45   $53.40  
  Purchase #7 $142.54   13.155%   $161.2911   $161.29   $161.30   $161.30  
  7 purchase totals = $926.74       $1,024.0016   $1,024.00   $1,024.05   $1,024.00