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 $30.55   4.783%   $32.0112   $32.01   $32.00   $32.00  
  Purchase #2 $214.50   10.343%   $236.6857   $236.69   $236.70   $236.70  
  Purchase #3 $65.44   13.524%   $74.2901   $74.29   $74.30   $74.30  
  Purchase #4 $160.28   3.702%   $166.2136   $166.21   $166.20   $166.20  
  Purchase #5 $209.40   5.383%   $220.672   $220.67   $220.65   $220.70  
  Purchase #6 $30.74   13.738%   $34.9631   $34.96   $34.95   $35.00  
  Purchase #7 $169.27   5.199%   $178.0703   $178.07   $178.05   $178.10  
  7 purchase totals = $880.18       $942.9060   $942.90   $942.85   $943.00