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 $36.91   11.629%   $41.2023   $41.20   $41.20   $41.20  
  Purchase #2 $54.43   11.172%   $60.5109   $60.51   $60.50   $60.50  
  Purchase #3 $221.96   3.666%   $230.0971   $230.10   $230.10   $230.10  
  Purchase #4 $77.99   8.766%   $84.8266   $84.83   $84.85   $84.80  
  Purchase #5 $160.42   4.397%   $167.4737   $167.47   $167.45   $167.50  
  Purchase #6 $216.49   4.823%   $226.9313   $226.93   $226.95   $226.90  
  Purchase #7 $203.64   10.545%   $225.1138   $225.11   $225.10   $225.10  
  7 purchase totals = $971.84       $1,036.1557   $1,036.15   $1,036.15   $1,036.10