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 $224.97   10.136%   $247.773   $247.77   $247.75   $247.80  
  Purchase #2 $119.49   5.486%   $126.0452   $126.05   $126.05   $126.00  
  Purchase #3 $85.75   9.701%   $94.0686   $94.07   $94.05   $94.10  
  Purchase #4 $39.96   9.742%   $43.8529   $43.85   $43.85   $43.90  
  Purchase #5 $181.42   7.702%   $195.393   $195.39   $195.40   $195.40  
  Purchase #6 $156.48   9.627%   $171.5443   $171.54   $171.55   $171.50  
  Purchase #7 $213.68   5.678%   $225.8128   $225.81   $225.80   $225.80  
  7 purchase totals = $1,021.75       $1,104.4898   $1,104.48   $1,104.45   $1,104.50