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 $62.78   7.140%   $67.2625   $67.26   $67.25   $67.30  
  Purchase #2 $161.83   10.829%   $179.3546   $179.35   $179.35   $179.40  
  Purchase #3 $209.66   8.186%   $226.8228   $226.82   $226.80   $226.80  
  Purchase #4 $223.56   9.580%   $244.977   $244.98   $245.00   $245.00  
  Purchase #5 $84.55   3.865%   $87.8179   $87.82   $87.80   $87.80  
  Purchase #6 $36.77   12.139%   $41.2335   $41.23   $41.25   $41.20  
  Purchase #7 $249.73   7.247%   $267.8279   $267.83   $267.85   $267.80  
  7 purchase totals = $1,028.88       $1,115.2962   $1,115.29   $1,115.30   $1,115.30