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 $77.65   13.280%   $87.9619   $87.96   $87.95   $88.00  
  Purchase #2 $201.97   7.824%   $217.7721   $217.77   $217.75   $217.80  
  Purchase #3 $226.45   11.702%   $252.9492   $252.95   $252.95   $252.90  
  Purchase #4 $48.89   8.659%   $53.1234   $53.12   $53.10   $53.10  
  Purchase #5 $83.47   5.475%   $88.04   $88.04   $88.05   $88.00  
  Purchase #6 $235.53   5.469%   $248.4111   $248.41   $248.40   $248.40  
  Purchase #7 $12.27   10.690%   $13.5817   $13.58   $13.60   $13.60  
  7 purchase totals = $886.23       $961.8394   $961.83   $961.80   $961.80