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 $163.42   8.283%   $176.9561   $176.96   $176.95   $177.00  
  Purchase #2 $242.75   11.650%   $271.0304   $271.03   $271.05   $271.00  
  Purchase #3 $216.52   5.638%   $228.7274   $228.73   $228.75   $228.70  
  Purchase #4 $225.97   9.522%   $247.4869   $247.49   $247.50   $247.50  
  Purchase #5 $248.51   9.768%   $272.7845   $272.78   $272.80   $272.80  
  Purchase #6 $140.32   8.295%   $151.9595   $151.96   $151.95   $152.00  
  Purchase #7 $55.67   7.823%   $60.0251   $60.03   $60.05   $60.00  
  7 purchase totals = $1,293.16       $1,408.9699   $1,408.98   $1,409.05   $1,409.00