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 $25.60   9.744%   $28.0945   $28.09   $28.10   $28.10  
  Purchase #2 $145.66   3.121%   $150.206   $150.21   $150.20   $150.20  
  Purchase #3 $90.35   4.558%   $94.4682   $94.47   $94.45   $94.50  
  Purchase #4 $89.95   4.258%   $93.7801   $93.78   $93.80   $93.80  
  Purchase #5 $63.85   7.208%   $68.4523   $68.45   $68.45   $68.50  
  Purchase #6 $105.61   13.480%   $119.8462   $119.85   $119.85   $119.80  
  Purchase #7 $37.90   9.254%   $41.4073   $41.41   $41.40   $41.40  
  7 purchase totals = $558.92       $596.2546   $596.26   $596.25   $596.30