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 $85.26   11.762%   $95.2883   $95.29   $95.30   $95.30  
  Purchase #2 $139.56   3.557%   $144.5241   $144.52   $144.50   $144.50  
  Purchase #3 $244.76   10.186%   $269.6913   $269.69   $269.70   $269.70  
  Purchase #4 $156.71   12.171%   $175.7832   $175.78   $175.80   $175.80  
  Purchase #5 $205.47   10.114%   $226.2512   $226.25   $226.25   $226.30  
  Purchase #6 $39.36   13.203%   $44.5567   $44.56   $44.55   $44.60  
  Purchase #7 $190.71   12.187%   $213.9518   $213.95   $213.95   $214.00  
  7 purchase totals = $1,061.83       $1,170.0466   $1,170.04   $1,170.05   $1,170.20