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 $208.52   10.674%   $230.7774   $230.78   $230.80   $230.80  
  Purchase #2 $182.64   4.804%   $191.414   $191.41   $191.40   $191.40  
  Purchase #3 $5.64   7.176%   $6.0447   $6.04   $6.05   $6.00  
  Purchase #4 $225.58   7.160%   $241.7315   $241.73   $241.75   $241.70  
  Purchase #5 $95.79   5.806%   $101.3516   $101.35   $101.35   $101.40  
  Purchase #6 $200.82   7.552%   $215.9859   $215.99   $216.00   $216.00  
  Purchase #7 $246.83   11.743%   $275.8152   $275.82   $275.80   $275.80  
  7 purchase totals = $1,165.82       $1,263.1203   $1,263.12   $1,263.15   $1,263.10