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 $23.53   6.424%   $25.0416   $25.04   $25.05   $25.00  
  Purchase #2 $210.41   13.578%   $238.9795   $238.98   $239.00   $239.00  
  Purchase #3 $117.26   7.717%   $126.309   $126.31   $126.30   $126.30  
  Purchase #4 $229.79   10.273%   $253.3963   $253.40   $253.40   $253.40  
  Purchase #5 $216.65   9.341%   $236.8873   $236.89   $236.90   $236.90  
  Purchase #6 $117.96   6.252%   $125.3349   $125.33   $125.35   $125.30  
  Purchase #7 $167.51   11.846%   $187.3532   $187.35   $187.35   $187.40  
  7 purchase totals = $1,083.11       $1,193.3018   $1,193.30   $1,193.35   $1,193.30