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 $53.68   3.623%   $55.6248   $55.62   $55.60   $55.60  
  Purchase #2 $191.27   13.550%   $217.1871   $217.19   $217.20   $217.20  
  Purchase #3 $27.62   8.163%   $29.8746   $29.87   $29.85   $29.90  
  Purchase #4 $111.67   9.494%   $122.2719   $122.27   $122.25   $122.30  
  Purchase #5 $177.74   8.302%   $192.496   $192.50   $192.50   $192.50  
  Purchase #6 $162.72   3.488%   $168.3957   $168.40   $168.40   $168.40  
  Purchase #7 $207.31   6.319%   $220.4099   $220.41   $220.40   $220.40  
  7 purchase totals = $932.01       $1,006.2600   $1,006.26   $1,006.20   $1,006.30