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 $88.34   9.208%   $96.4743   $96.47   $96.45   $96.50  
  Purchase #2 $60.40   7.516%   $64.9397   $64.94   $64.95   $64.90  
  Purchase #3 $116.47   10.677%   $128.9055   $128.91   $128.90   $128.90  
  Purchase #4 $31.79   7.278%   $34.1037   $34.10   $34.10   $34.10  
  Purchase #5 $210.39   10.802%   $233.1163   $233.12   $233.10   $233.10  
  Purchase #6 $241.95   10.857%   $268.2185   $268.22   $268.20   $268.20  
  Purchase #7 $25.92   4.300%   $27.0346   $27.03   $27.05   $27.00  
  7 purchase totals = $775.26       $852.7926   $852.79   $852.75   $852.70