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 $89.98   3.818%   $93.4154   $93.42   $93.40   $93.40  
  Purchase #2 $200.67   5.415%   $211.5363   $211.54   $211.55   $211.50  
  Purchase #3 $201.66   5.543%   $212.838   $212.84   $212.85   $212.80  
  Purchase #4 $101.44   10.582%   $112.1744   $112.17   $112.15   $112.20  
  Purchase #5 $250.42   8.213%   $270.987   $270.99   $271.00   $271.00  
  Purchase #6 $158.70   9.182%   $173.2718   $173.27   $173.25   $173.30  
  Purchase #7 $40.97   10.733%   $45.3673   $45.37   $45.35   $45.40  
  7 purchase totals = $1,043.84       $1,119.5902   $1,119.60   $1,119.55   $1,119.60