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 $236.54   6.553%   $252.0405   $252.04   $252.05   $252.00  
  Purchase #2 $41.35   11.510%   $46.1094   $46.11   $46.10   $46.10  
  Purchase #3 $101.30   8.288%   $109.6957   $109.70   $109.70   $109.70  
  Purchase #4 $131.64   10.396%   $145.3253   $145.33   $145.35   $145.30  
  Purchase #5 $75.87   10.447%   $83.7961   $83.80   $83.80   $83.80  
  Purchase #6 $79.98   3.192%   $82.533   $82.53   $82.55   $82.50  
  Purchase #7 $186.50   10.474%   $206.034   $206.03   $206.05   $206.00  
  7 purchase totals = $853.18       $925.5340   $925.54   $925.60   $925.40