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 $69.40   5.681%   $73.3426   $73.34   $73.35   $73.30  
  Purchase #2 $133.61   10.249%   $147.3037   $147.30   $147.30   $147.30  
  Purchase #3 $100.82   8.522%   $109.4119   $109.41   $109.40   $109.40  
  Purchase #4 $169.80   12.869%   $191.6516   $191.65   $191.65   $191.70  
  Purchase #5 $212.33   3.701%   $220.1883   $220.19   $220.20   $220.20  
  Purchase #6 $141.71   8.176%   $153.2962   $153.30   $153.30   $153.30  
  Purchase #7 $51.50   10.703%   $57.012   $57.01   $57.00   $57.00  
  7 purchase totals = $879.17       $952.2063   $952.20   $952.20   $952.20