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 $59.81   8.253%   $64.7461   $64.75   $64.75   $64.70  
  Purchase #2 $82.62   11.259%   $91.9222   $91.92   $91.90   $91.90  
  Purchase #3 $21.75   13.527%   $24.6921   $24.69   $24.70   $24.70  
  Purchase #4 $120.58   5.106%   $126.7368   $126.74   $126.75   $126.70  
  Purchase #5 $169.66   13.717%   $192.9323   $192.93   $192.95   $192.90  
  Purchase #6 $148.78   10.749%   $164.7724   $164.77   $164.75   $164.80  
  Purchase #7 $31.69   11.350%   $35.2868   $35.29   $35.30   $35.30  
  7 purchase totals = $634.89       $701.0887   $701.09   $701.10   $701.00