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 $54.76   10.637%   $60.5848   $60.58   $60.60   $60.60  
  Purchase #2 $118.53   8.151%   $128.1914   $128.19   $128.20   $128.20  
  Purchase #3 $179.41   8.723%   $195.0599   $195.06   $195.05   $195.10  
  Purchase #4 $235.30   5.851%   $249.0674   $249.07   $249.05   $249.10  
  Purchase #5 $247.51   3.658%   $256.5639   $256.56   $256.55   $256.60  
  Purchase #6 $88.26   11.407%   $98.3278   $98.33   $98.35   $98.30  
  Purchase #7 $86.64   11.829%   $96.8886   $96.89   $96.90   $96.90  
  7 purchase totals = $1,010.41       $1,084.6838   $1,084.68   $1,084.70   $1,084.80