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 $241.81   8.359%   $262.0229   $262.02   $262.00   $262.00  
  Purchase #2 $29.71   6.103%   $31.5232   $31.52   $31.50   $31.50  
  Purchase #3 $172.61   9.755%   $189.4481   $189.45   $189.45   $189.40  
  Purchase #4 $47.91   13.426%   $54.3424   $54.34   $54.35   $54.30  
  Purchase #5 $53.78   12.521%   $60.5138   $60.51   $60.50   $60.50  
  Purchase #6 $226.69   7.566%   $243.8414   $243.84   $243.85   $243.80  
  Purchase #7 $86.57   7.553%   $93.1086   $93.11   $93.10   $93.10  
  7 purchase totals = $859.08       $934.8004   $934.79   $934.75   $934.60