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 $203.60   11.406%   $226.8226   $226.82   $226.80   $226.80  
  Purchase #2 $11.36   12.600%   $12.7914   $12.79   $12.80   $12.80  
  Purchase #3 $158.56   4.656%   $165.9426   $165.94   $165.95   $165.90  
  Purchase #4 $176.92   12.350%   $198.7696   $198.77   $198.75   $198.80  
  Purchase #5 $132.89   13.677%   $151.0654   $151.07   $151.05   $151.10  
  Purchase #6 $152.97   6.294%   $162.5979   $162.60   $162.60   $162.60  
  Purchase #7 $240.71   4.136%   $250.6658   $250.67   $250.65   $250.70  
  7 purchase totals = $1,077.01       $1,168.6553   $1,168.66   $1,168.60   $1,168.70