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 $66.70   3.517%   $69.0458   $69.05   $69.05   $69.00  
  Purchase #2 $101.64   9.726%   $111.5255   $111.53   $111.55   $111.50  
  Purchase #3 $192.72   3.465%   $199.3977   $199.40   $199.40   $199.40  
  Purchase #4 $139.78   4.378%   $145.8996   $145.90   $145.90   $145.90  
  Purchase #5 $175.48   11.198%   $195.1303   $195.13   $195.15   $195.10  
  Purchase #6 $167.26   4.861%   $175.3905   $175.39   $175.40   $175.40  
  Purchase #7 $246.63   11.140%   $274.1046   $274.10   $274.10   $274.10  
  7 purchase totals = $1,090.21       $1,170.4940   $1,170.50   $1,170.55   $1,170.40