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 $68.73   6.489%   $73.1899   $73.19   $73.20   $73.20  
  Purchase #2 $229.89   9.155%   $250.9364   $250.94   $250.95   $250.90  
  Purchase #3 $190.80   8.132%   $206.3159   $206.32   $206.30   $206.30  
  Purchase #4 $177.32   13.260%   $200.8326   $200.83   $200.85   $200.80  
  Purchase #5 $243.41   5.110%   $255.8483   $255.85   $255.85   $255.80  
  Purchase #6 $178.30   11.432%   $198.6833   $198.68   $198.70   $198.70  
  Purchase #7 $82.39   13.799%   $93.759   $93.76   $93.75   $93.80  
  7 purchase totals = $1,170.84       $1,279.5654   $1,279.57   $1,279.60   $1,279.50