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 $88.68   7.797%   $95.5944   $95.59   $95.60   $95.60  
  Purchase #2 $229.29   9.149%   $250.2677   $250.27   $250.25   $250.30  
  Purchase #3 $29.26   5.791%   $30.9544   $30.95   $30.95   $31.00  
  Purchase #4 $199.83   3.740%   $207.3036   $207.30   $207.30   $207.30  
  Purchase #5 $100.48   8.339%   $108.859   $108.86   $108.85   $108.90  
  Purchase #6 $94.29   12.632%   $106.2007   $106.20   $106.20   $106.20  
  Purchase #7 $80.79   10.516%   $89.2859   $89.29   $89.30   $89.30  
  7 purchase totals = $822.62       $888.4657   $888.46   $888.45   $888.60