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 $226.93   7.501%   $243.952   $243.95   $243.95   $244.00  
  Purchase #2 $191.25   11.634%   $213.5   $213.50   $213.50   $213.50  
  Purchase #3 $135.83   3.263%   $140.2621   $140.26   $140.25   $140.30  
  Purchase #4 $247.88   11.149%   $275.5161   $275.52   $275.50   $275.50  
  Purchase #5 $176.60   8.343%   $191.3337   $191.33   $191.35   $191.30  
  Purchase #6 $85.69   13.118%   $96.9308   $96.93   $96.95   $96.90  
  Purchase #7 $77.37   7.330%   $83.0412   $83.04   $83.05   $83.00  
  7 purchase totals = $1,141.55       $1,244.5359   $1,244.53   $1,244.55   $1,244.50