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 $190.44   5.827%   $201.5369   $201.54   $201.55   $201.50  
  Purchase #2 $205.52   9.365%   $224.7669   $224.77   $224.75   $224.80  
  Purchase #3 $235.88   8.151%   $255.1066   $255.11   $255.10   $255.10  
  Purchase #4 $162.67   7.230%   $174.431   $174.43   $174.45   $174.40  
  Purchase #5 $17.35   3.753%   $18.0011   $18.00   $18.00   $18.00  
  Purchase #6 $109.27   3.689%   $113.301   $113.30   $113.30   $113.30  
  Purchase #7 $194.71   11.726%   $217.5417   $217.54   $217.55   $217.50  
  7 purchase totals = $1,115.84       $1,204.6852   $1,204.69   $1,204.70   $1,204.60