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 $242.54   8.424%   $262.9716   $262.97   $262.95   $263.00  
  Purchase #2 $206.33   8.411%   $223.6844   $223.68   $223.70   $223.70  
  Purchase #3 $235.31   9.867%   $258.528   $258.53   $258.55   $258.50  
  Purchase #4 $59.70   9.814%   $65.559   $65.56   $65.55   $65.60  
  Purchase #5 $57.84   12.122%   $64.8514   $64.85   $64.85   $64.90  
  Purchase #6 $132.77   8.180%   $143.6306   $143.63   $143.65   $143.60  
  Purchase #7 $214.92   11.700%   $240.0656   $240.07   $240.05   $240.10  
  7 purchase totals = $1,149.41       $1,259.2906   $1,259.29   $1,259.30   $1,259.40