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 $229.66   3.617%   $237.9668   $237.97   $237.95   $238.00  
  Purchase #2 $32.73   10.647%   $36.2148   $36.21   $36.20   $36.20  
  Purchase #3 $245.49   9.262%   $268.2273   $268.23   $268.25   $268.20  
  Purchase #4 $196.55   10.393%   $216.9774   $216.98   $217.00   $217.00  
  Purchase #5 $150.55   12.211%   $168.9337   $168.93   $168.95   $168.90  
  Purchase #6 $9.68   11.215%   $10.7656   $10.77   $10.75   $10.80  
  Purchase #7 $85.53   11.769%   $95.596   $95.60   $95.60   $95.60  
  7 purchase totals = $950.19       $1,034.6816   $1,034.69   $1,034.70   $1,034.70