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 $238.84   7.412%   $256.5428   $256.54   $256.55   $256.50  
  Purchase #2 $114.57   6.636%   $122.1729   $122.17   $122.15   $122.20  
  Purchase #3 $30.29   8.333%   $32.8141   $32.81   $32.80   $32.80  
  Purchase #4 $227.48   13.487%   $258.1602   $258.16   $258.15   $258.20  
  Purchase #5 $26.49   11.353%   $29.4974   $29.50   $29.50   $29.50  
  Purchase #6 $211.78   10.271%   $233.5319   $233.53   $233.55   $233.50  
  Purchase #7 $86.64   8.512%   $94.0148   $94.01   $94.00   $94.00  
  7 purchase totals = $936.09       $1,026.7341   $1,026.72   $1,026.70   $1,026.70