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 $41.82   10.780%   $46.3282   $46.33   $46.35   $46.30  
  Purchase #2 $99.62   12.329%   $111.9021   $111.90   $111.90   $111.90  
  Purchase #3 $60.56   5.312%   $63.7769   $63.78   $63.80   $63.80  
  Purchase #4 $213.57   8.476%   $231.6722   $231.67   $231.65   $231.70  
  Purchase #5 $136.34   6.167%   $144.7481   $144.75   $144.75   $144.70  
  Purchase #6 $227.33   6.343%   $241.7495   $241.75   $241.75   $241.70  
  Purchase #7 $192.36   13.163%   $217.6803   $217.68   $217.70   $217.70  
  7 purchase totals = $971.60       $1,057.8573   $1,057.86   $1,057.90   $1,057.80