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 $135.34   8.401%   $146.7099   $146.71   $146.70   $146.70  
  Purchase #2 $171.49   10.205%   $188.9906   $188.99   $189.00   $189.00  
  Purchase #3 $8.90   10.342%   $9.8204   $9.82   $9.80   $9.80  
  Purchase #4 $63.33   10.564%   $70.0202   $70.02   $70.00   $70.00  
  Purchase #5 $159.68   4.720%   $167.2169   $167.22   $167.20   $167.20  
  Purchase #6 $204.86   9.346%   $224.0062   $224.01   $224.00   $224.00  
  Purchase #7 $219.43   3.311%   $226.6953   $226.70   $226.70   $226.70  
  7 purchase totals = $963.03       $1,033.4595   $1,033.47   $1,033.40   $1,033.40