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 $131.78   13.800%   $149.9656   $149.97   $149.95   $150.00  
  Purchase #2 $125.89   13.119%   $142.4055   $142.41   $142.40   $142.40  
  Purchase #3 $33.41   4.672%   $34.9709   $34.97   $34.95   $35.00  
  Purchase #4 $117.54   9.698%   $128.939   $128.94   $128.95   $128.90  
  Purchase #5 $209.96   11.597%   $234.3091   $234.31   $234.30   $234.30  
  Purchase #6 $162.54   9.850%   $178.5502   $178.55   $178.55   $178.60  
  Purchase #7 $169.63   3.673%   $175.8605   $175.86   $175.85   $175.90  
  7 purchase totals = $950.75       $1,045.0008   $1,045.01   $1,044.95   $1,045.10