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 $111.34   13.722%   $126.6181   $126.62   $126.60   $126.60  
  Purchase #2 $151.71   10.424%   $167.5243   $167.52   $167.50   $167.50  
  Purchase #3 $56.66   8.355%   $61.3939   $61.39   $61.40   $61.40  
  Purchase #4 $145.59   12.191%   $163.3389   $163.34   $163.35   $163.30  
  Purchase #5 $28.36   12.795%   $31.9887   $31.99   $32.00   $32.00  
  Purchase #6 $239.26   6.419%   $254.6181   $254.62   $254.60   $254.60  
  Purchase #7 $151.51   6.235%   $160.9566   $160.96   $160.95   $161.00  
  7 purchase totals = $884.43       $966.4386   $966.44   $966.40   $966.40