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 $205.90   8.663%   $223.7371   $223.74   $223.75   $223.70  
  Purchase #2 $179.39   10.202%   $197.6914   $197.69   $197.70   $197.70  
  Purchase #3 $107.43   10.312%   $118.5082   $118.51   $118.50   $118.50  
  Purchase #4 $200.53   5.569%   $211.6975   $211.70   $211.70   $211.70  
  Purchase #5 $127.92   4.440%   $133.5996   $133.60   $133.60   $133.60  
  Purchase #6 $165.62   9.499%   $181.3522   $181.35   $181.35   $181.40  
  Purchase #7 $195.28   7.421%   $209.7717   $209.77   $209.75   $209.80  
  7 purchase totals = $1,182.07       $1,276.3577   $1,276.36   $1,276.35   $1,276.40