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 $114.81   10.212%   $126.5344   $126.53   $126.55   $126.50  
  Purchase #2 $235.41   3.596%   $243.8753   $243.88   $243.90   $243.90  
  Purchase #3 $141.96   13.829%   $161.5916   $161.59   $161.60   $161.60  
  Purchase #4 $90.87   7.492%   $97.678   $97.68   $97.70   $97.70  
  Purchase #5 $170.46   13.796%   $193.9767   $193.98   $194.00   $194.00  
  Purchase #6 $70.51   12.434%   $79.2772   $79.28   $79.30   $79.30  
  Purchase #7 $95.67   9.474%   $104.7338   $104.73   $104.75   $104.70  
  7 purchase totals = $919.69       $1,007.6670   $1,007.67   $1,007.80   $1,007.70