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 $52.37   12.272%   $58.7968   $58.80   $58.80   $58.80  
  Purchase #2 $220.82   9.459%   $241.7074   $241.71   $241.70   $241.70  
  Purchase #3 $74.33   12.821%   $83.8598   $83.86   $83.85   $83.90  
  Purchase #4 $249.56   8.464%   $270.6828   $270.68   $270.70   $270.70  
  Purchase #5 $93.53   10.660%   $103.5003   $103.50   $103.50   $103.50  
  Purchase #6 $232.57   5.863%   $246.2056   $246.21   $246.20   $246.20  
  Purchase #7 $75.64   7.150%   $81.0483   $81.05   $81.05   $81.00  
  7 purchase totals = $998.82       $1,085.8010   $1,085.81   $1,085.80   $1,085.80