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 $65.49   12.601%   $73.7424   $73.74   $73.75   $73.70  
  Purchase #2 $121.71   4.271%   $126.9082   $126.91   $126.90   $126.90  
  Purchase #3 $124.74   6.672%   $133.0627   $133.06   $133.05   $133.10  
  Purchase #4 $24.56   4.246%   $25.6028   $25.60   $25.60   $25.60  
  Purchase #5 $149.77   9.286%   $163.6776   $163.68   $163.70   $163.70  
  Purchase #6 $179.75   6.820%   $192.009   $192.01   $192.00   $192.00  
  Purchase #7 $191.86   7.553%   $206.3512   $206.35   $206.35   $206.40  
  7 purchase totals = $857.88       $921.3539   $921.35   $921.35   $921.40