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 $232.85   8.320%   $252.2231   $252.22   $252.20   $252.20  
  Purchase #2 $195.32   9.385%   $213.6508   $213.65   $213.65   $213.70  
  Purchase #3 $240.96   6.838%   $257.4368   $257.44   $257.45   $257.40  
  Purchase #4 $107.77   4.350%   $112.458   $112.46   $112.45   $112.50  
  Purchase #5 $164.85   13.813%   $187.6207   $187.62   $187.60   $187.60  
  Purchase #6 $27.65   4.713%   $28.9531   $28.95   $28.95   $29.00  
  Purchase #7 $43.95   13.692%   $49.9676   $49.97   $49.95   $50.00  
  7 purchase totals = $1,013.35       $1,102.3101   $1,102.31   $1,102.25   $1,102.40