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 $201.83   8.102%   $218.1823   $218.18   $218.20   $218.20  
  Purchase #2 $69.75   8.468%   $75.6564   $75.66   $75.65   $75.70  
  Purchase #3 $109.35   8.824%   $118.999   $119.00   $119.00   $119.00  
  Purchase #4 $34.46   6.815%   $36.8084   $36.81   $36.80   $36.80  
  Purchase #5 $244.78   4.126%   $254.8796   $254.88   $254.90   $254.90  
  Purchase #6 $158.45   11.196%   $176.1901   $176.19   $176.20   $176.20  
  Purchase #7 $129.93   13.222%   $147.1093   $147.11   $147.10   $147.10  
  7 purchase totals = $948.55       $1,027.8251   $1,027.83   $1,027.85   $1,027.90