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 $187.91   8.793%   $204.4329   $204.43   $204.45   $204.40  
  Purchase #2 $47.67   13.383%   $54.0497   $54.05   $54.05   $54.00  
  Purchase #3 $230.85   6.556%   $245.9845   $245.98   $246.00   $246.00  
  Purchase #4 $200.40   10.251%   $220.943   $220.94   $220.95   $220.90  
  Purchase #5 $87.79   5.733%   $92.823   $92.82   $92.80   $92.80  
  Purchase #6 $137.57   8.631%   $149.4437   $149.44   $149.45   $149.40  
  Purchase #7 $162.84   13.107%   $184.1834   $184.18   $184.20   $184.20  
  7 purchase totals = $1,055.03       $1,151.8602   $1,151.84   $1,151.90   $1,151.70