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 $69.49   3.406%   $71.8568   $71.86   $71.85   $71.90  
  Purchase #2 $222.50   10.722%   $246.3565   $246.36   $246.35   $246.40  
  Purchase #3 $18.53   11.396%   $20.6417   $20.64   $20.65   $20.60  
  Purchase #4 $88.29   9.231%   $96.44   $96.44   $96.45   $96.40  
  Purchase #5 $73.76   5.713%   $77.9739   $77.97   $77.95   $78.00  
  Purchase #6 $240.39   5.790%   $254.3086   $254.31   $254.30   $254.30  
  Purchase #7 $224.61   13.193%   $254.2428   $254.24   $254.25   $254.20  
  7 purchase totals = $937.57       $1,021.8203   $1,021.82   $1,021.80   $1,021.80