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 $205.38   6.785%   $219.315   $219.32   $219.30   $219.30  
  Purchase #2 $101.67   8.442%   $110.253   $110.25   $110.25   $110.30  
  Purchase #3 $163.83   3.141%   $168.9759   $168.98   $169.00   $169.00  
  Purchase #4 $95.61   3.479%   $98.9363   $98.94   $98.95   $98.90  
  Purchase #5 $179.46   6.133%   $190.4663   $190.47   $190.45   $190.50  
  Purchase #6 $80.31   3.367%   $83.014   $83.01   $83.00   $83.00  
  Purchase #7 $56.93   6.828%   $60.8172   $60.82   $60.80   $60.80  
  7 purchase totals = $883.19       $931.7777   $931.79   $931.75   $931.80