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 $89.93   10.133%   $99.0426   $99.04   $99.05   $99.00  
  Purchase #2 $230.88   8.609%   $250.7565   $250.76   $250.75   $250.80  
  Purchase #3 $43.27   13.451%   $49.0902   $49.09   $49.10   $49.10  
  Purchase #4 $126.98   11.210%   $141.2145   $141.21   $141.20   $141.20  
  Purchase #5 $22.91   7.390%   $24.603   $24.60   $24.60   $24.60  
  Purchase #6 $156.46   13.786%   $178.0296   $178.03   $178.05   $178.00  
  Purchase #7 $223.43   8.447%   $242.3031   $242.30   $242.30   $242.30  
  7 purchase totals = $893.86       $985.0395   $985.03   $985.05   $985.00