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 $57.69   8.565%   $62.6311   $62.63   $62.65   $62.60  
  Purchase #2 $70.39   6.505%   $74.9689   $74.97   $74.95   $75.00  
  Purchase #3 $247.48   10.764%   $274.1187   $274.12   $274.10   $274.10  
  Purchase #4 $174.61   11.618%   $194.8962   $194.90   $194.90   $194.90  
  Purchase #5 $225.52   7.242%   $241.8522   $241.85   $241.85   $241.90  
  Purchase #6 $9.97   5.166%   $10.4851   $10.49   $10.50   $10.50  
  Purchase #7 $134.57   7.149%   $144.1904   $144.19   $144.20   $144.20  
  7 purchase totals = $920.23       $1,003.1426   $1,003.15   $1,003.15   $1,003.20