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 $126.79   3.332%   $131.0146   $131.01   $131.00   $131.00  
  Purchase #2 $94.95   12.709%   $107.0172   $107.02   $107.00   $107.00  
  Purchase #3 $119.90   8.765%   $130.4092   $130.41   $130.40   $130.40  
  Purchase #4 $203.68   9.294%   $222.61   $222.61   $222.60   $222.60  
  Purchase #5 $49.71   3.662%   $51.5304   $51.53   $51.55   $51.50  
  Purchase #6 $233.44   5.832%   $247.0542   $247.05   $247.05   $247.10  
  Purchase #7 $165.99   5.858%   $175.7137   $175.71   $175.70   $175.70  
  7 purchase totals = $994.46       $1,065.3493   $1,065.34   $1,065.30   $1,065.30