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 $177.52   11.218%   $197.4342   $197.43   $197.45   $197.40  
  Purchase #2 $154.59   7.183%   $165.6942   $165.69   $165.70   $165.70  
  Purchase #3 $138.93   13.782%   $158.0773   $158.08   $158.10   $158.10  
  Purchase #4 $236.87   11.236%   $263.4847   $263.48   $263.50   $263.50  
  Purchase #5 $72.94   6.741%   $77.8569   $77.86   $77.85   $77.90  
  Purchase #6 $201.68   3.853%   $209.4507   $209.45   $209.45   $209.50  
  Purchase #7 $229.25   10.865%   $254.158   $254.16   $254.15   $254.20  
  7 purchase totals = $1,211.78       $1,326.1560   $1,326.15   $1,326.20   $1,326.30