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 $56.92   11.339%   $63.3742   $63.37   $63.35   $63.40  
  Purchase #2 $200.42   6.125%   $212.6957   $212.70   $212.70   $212.70  
  Purchase #3 $198.99   5.500%   $209.9345   $209.93   $209.95   $209.90  
  Purchase #4 $247.42   10.545%   $273.5104   $273.51   $273.50   $273.50  
  Purchase #5 $46.68   9.495%   $51.1123   $51.11   $51.10   $51.10  
  Purchase #6 $179.39   11.168%   $199.4243   $199.42   $199.40   $199.40  
  Purchase #7 $111.56   13.712%   $126.8571   $126.86   $126.85   $126.90  
  7 purchase totals = $1,041.38       $1,136.9085   $1,136.90   $1,136.85   $1,136.90