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 $221.95   13.563%   $252.0531   $252.05   $252.05   $252.10  
  Purchase #2 $144.90   9.235%   $158.2815   $158.28   $158.30   $158.30  
  Purchase #3 $222.56   3.519%   $230.3919   $230.39   $230.40   $230.40  
  Purchase #4 $201.43   6.343%   $214.2067   $214.21   $214.20   $214.20  
  Purchase #5 $69.52   8.464%   $75.4042   $75.40   $75.40   $75.40  
  Purchase #6 $228.68   11.355%   $254.6466   $254.65   $254.65   $254.60  
  Purchase #7 $75.65   4.406%   $78.9831   $78.98   $79.00   $79.00  
  7 purchase totals = $1,164.69       $1,263.9671   $1,263.96   $1,264.00   $1,264.00