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 $165.48   8.132%   $178.9368   $178.94   $178.95   $178.90  
  Purchase #2 $82.87   11.145%   $92.1059   $92.11   $92.10   $92.10  
  Purchase #3 $216.95   3.116%   $223.7102   $223.71   $223.70   $223.70  
  Purchase #4 $244.43   8.123%   $264.285   $264.29   $264.30   $264.30  
  Purchase #5 $236.39   13.592%   $268.5201   $268.52   $268.50   $268.50  
  Purchase #6 $222.97   7.491%   $239.6727   $239.67   $239.65   $239.70  
  Purchase #7 $80.76   13.762%   $91.8742   $91.87   $91.85   $91.90  
  7 purchase totals = $1,249.85       $1,359.1049   $1,359.11   $1,359.05   $1,359.10