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 $246.44   11.598%   $275.0221   $275.02   $275.00   $275.00  
  Purchase #2 $20.31   12.651%   $22.8794   $22.88   $22.90   $22.90  
  Purchase #3 $25.31   4.262%   $26.3887   $26.39   $26.40   $26.40  
  Purchase #4 $246.33   6.519%   $262.3883   $262.39   $262.40   $262.40  
  Purchase #5 $120.90   10.476%   $133.5655   $133.57   $133.55   $133.60  
  Purchase #6 $148.49   13.577%   $168.6505   $168.65   $168.65   $168.70  
  Purchase #7 $148.84   12.292%   $167.1354   $167.14   $167.15   $167.10  
  7 purchase totals = $956.62       $1,056.0299   $1,056.04   $1,056.05   $1,056.10