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 $58.44   4.352%   $60.9833   $60.98   $61.00   $61.00  
  Purchase #2 $91.68   6.872%   $97.9802   $97.98   $98.00   $98.00  
  Purchase #3 $227.70   7.598%   $245.0006   $245.00   $245.00   $245.00  
  Purchase #4 $231.46   5.485%   $244.1556   $244.16   $244.15   $244.20  
  Purchase #5 $219.55   11.566%   $244.9432   $244.94   $244.95   $244.90  
  Purchase #6 $176.85   5.639%   $186.8226   $186.82   $186.80   $186.80  
  Purchase #7 $129.54   9.471%   $141.8087   $141.81   $141.80   $141.80  
  7 purchase totals = $1,135.22       $1,221.6942   $1,221.69   $1,221.70   $1,221.70