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 $73.52   3.662%   $76.2123   $76.21   $76.20   $76.20  
  Purchase #2 $240.70   3.872%   $250.0199   $250.02   $250.00   $250.00  
  Purchase #3 $109.31   9.124%   $119.2834   $119.28   $119.30   $119.30  
  Purchase #4 $243.34   6.342%   $258.7726   $258.77   $258.75   $258.80  
  Purchase #5 $183.55   6.572%   $195.6129   $195.61   $195.60   $195.60  
  Purchase #6 $49.98   11.415%   $55.6852   $55.69   $55.70   $55.70  
  Purchase #7 $204.51   5.477%   $215.711   $215.71   $215.70   $215.70  
  7 purchase totals = $1,104.91       $1,171.2973   $1,171.29   $1,171.25   $1,171.30