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 $202.68   12.160%   $227.3259   $227.33   $227.35   $227.30  
  Purchase #2 $149.95   9.214%   $163.7664   $163.77   $163.75   $163.80  
  Purchase #3 $36.63   13.695%   $41.6465   $41.65   $41.65   $41.60  
  Purchase #4 $174.98   13.492%   $198.5883   $198.59   $198.60   $198.60  
  Purchase #5 $210.34   10.622%   $232.6823   $232.68   $232.70   $232.70  
  Purchase #6 $85.76   11.248%   $95.4063   $95.41   $95.40   $95.40  
  Purchase #7 $46.62   9.404%   $51.0041   $51.00   $51.00   $51.00  
  7 purchase totals = $906.96       $1,010.4198   $1,010.43   $1,010.45   $1,010.40