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 $216.96   11.497%   $241.9039   $241.90   $241.90   $241.90  
  Purchase #2 $224.91   7.572%   $241.9402   $241.94   $241.95   $241.90  
  Purchase #3 $12.84   13.196%   $14.5344   $14.53   $14.55   $14.50  
  Purchase #4 $178.29   10.565%   $197.1263   $197.13   $197.15   $197.10  
  Purchase #5 $63.33   8.190%   $68.5167   $68.52   $68.50   $68.50  
  Purchase #6 $67.49   7.111%   $72.2892   $72.29   $72.30   $72.30  
  Purchase #7 $68.63   13.171%   $77.6693   $77.67   $77.65   $77.70  
  7 purchase totals = $832.45       $913.9800   $913.98   $914.00   $913.90