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 $69.29   6.512%   $73.8022   $73.80   $73.80   $73.80  
  Purchase #2 $160.42   6.405%   $170.6949   $170.69   $170.70   $170.70  
  Purchase #3 $51.76   11.497%   $57.7108   $57.71   $57.70   $57.70  
  Purchase #4 $186.50   5.452%   $196.668   $196.67   $196.65   $196.70  
  Purchase #5 $183.52   6.513%   $195.4727   $195.47   $195.45   $195.50  
  Purchase #6 $83.45   7.175%   $89.4375   $89.44   $89.45   $89.40  
  Purchase #7 $191.34   6.774%   $204.3014   $204.30   $204.30   $204.30  
  7 purchase totals = $926.28       $988.0875   $988.08   $988.05   $988.10