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 $55.66   5.302%   $58.6111   $58.61   $58.60   $58.60  
  Purchase #2 $234.39   8.388%   $254.0506   $254.05   $254.05   $254.10  
  Purchase #3 $208.34   5.230%   $219.2362   $219.24   $219.25   $219.20  
  Purchase #4 $159.31   13.737%   $181.1944   $181.19   $181.20   $181.20  
  Purchase #5 $151.85   13.205%   $171.9018   $171.90   $171.90   $171.90  
  Purchase #6 $75.26   9.686%   $82.5497   $82.55   $82.55   $82.50  
  Purchase #7 $39.51   13.355%   $44.7866   $44.79   $44.80   $44.80  
  7 purchase totals = $924.32       $1,012.3304   $1,012.33   $1,012.35   $1,012.30