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 $72.89   13.454%   $82.6966   $82.70   $82.70   $82.70  
  Purchase #2 $248.62   4.577%   $259.9993   $260.00   $260.00   $260.00  
  Purchase #3 $235.85   8.525%   $255.9562   $255.96   $255.95   $256.00  
  Purchase #4 $198.55   8.372%   $215.1726   $215.17   $215.15   $215.20  
  Purchase #5 $93.79   6.148%   $99.5562   $99.56   $99.55   $99.60  
  Purchase #6 $81.44   12.419%   $91.554   $91.55   $91.55   $91.60  
  Purchase #7 $238.99   3.107%   $246.4154   $246.42   $246.40   $246.40  
  7 purchase totals = $1,170.13       $1,251.3503   $1,251.36   $1,251.30   $1,251.50