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 $227.25   8.234%   $245.9618   $245.96   $245.95   $246.00  
  Purchase #2 $91.75   7.222%   $98.3762   $98.38   $98.40   $98.40  
  Purchase #3 $167.47   6.498%   $178.3522   $178.35   $178.35   $178.40  
  Purchase #4 $37.83   10.797%   $41.9145   $41.91   $41.90   $41.90  
  Purchase #5 $133.35   5.844%   $141.143   $141.14   $141.15   $141.10  
  Purchase #6 $165.64   13.400%   $187.8358   $187.84   $187.85   $187.80  
  Purchase #7 $22.61   10.531%   $24.9911   $24.99   $25.00   $25.00  
  7 purchase totals = $845.90       $918.5746   $918.57   $918.60   $918.60