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 $76.48   6.310%   $81.3059   $81.31   $81.30   $81.30  
  Purchase #2 $160.93   11.343%   $179.1843   $179.18   $179.20   $179.20  
  Purchase #3 $54.97   13.823%   $62.5685   $62.57   $62.55   $62.60  
  Purchase #4 $168.44   6.225%   $178.9254   $178.93   $178.95   $178.90  
  Purchase #5 $176.34   3.802%   $183.0444   $183.04   $183.05   $183.00  
  Purchase #6 $61.44   4.362%   $64.12   $64.12   $64.10   $64.10  
  Purchase #7 $232.94   6.206%   $247.3963   $247.40   $247.40   $247.40  
  7 purchase totals = $931.54       $996.5448   $996.55   $996.55   $996.50