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 $203.84   11.821%   $227.9359   $227.94   $227.95   $227.90  
  Purchase #2 $177.95   11.848%   $199.0335   $199.03   $199.05   $199.00  
  Purchase #3 $22.31   11.168%   $24.8016   $24.80   $24.80   $24.80  
  Purchase #4 $241.59   11.157%   $268.5442   $268.54   $268.55   $268.50  
  Purchase #5 $89.62   8.637%   $97.3605   $97.36   $97.35   $97.40  
  Purchase #6 $30.75   4.543%   $32.147   $32.15   $32.15   $32.10  
  Purchase #7 $141.31   12.594%   $159.1066   $159.11   $159.10   $159.10  
  7 purchase totals = $907.37       $1,008.9293   $1,008.93   $1,008.95   $1,008.80