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 $32.86   6.230%   $34.9072   $34.91   $34.90   $34.90  
  Purchase #2 $184.52   7.167%   $197.7445   $197.74   $197.75   $197.70  
  Purchase #3 $33.46   9.416%   $36.6106   $36.61   $36.60   $36.60  
  Purchase #4 $201.40   5.496%   $212.4689   $212.47   $212.45   $212.50  
  Purchase #5 $165.92   7.391%   $178.1831   $178.18   $178.20   $178.20  
  Purchase #6 $120.39   5.788%   $127.3582   $127.36   $127.35   $127.40  
  Purchase #7 $157.52   11.170%   $175.115   $175.12   $175.10   $175.10  
  7 purchase totals = $896.07       $962.3875   $962.39   $962.35   $962.40