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 $218.83   11.821%   $244.6979   $244.70   $244.70   $244.70  
  Purchase #2 $64.81   10.128%   $71.374   $71.37   $71.35   $71.40  
  Purchase #3 $54.39   3.855%   $56.4867   $56.49   $56.50   $56.50  
  Purchase #4 $10.39   12.381%   $11.6764   $11.68   $11.70   $11.70  
  Purchase #5 $174.86   11.451%   $194.8832   $194.88   $194.90   $194.90  
  Purchase #6 $148.58   12.430%   $167.0485   $167.05   $167.05   $167.00  
  Purchase #7 $32.98   9.208%   $36.0168   $36.02   $36.00   $36.00  
  7 purchase totals = $704.84       $782.1835   $782.19   $782.20   $782.20