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 $244.89   12.145%   $274.6319   $274.63   $274.65   $274.60  
  Purchase #2 $194.92   3.456%   $201.6564   $201.66   $201.65   $201.70  
  Purchase #3 $204.80   10.336%   $225.9681   $225.97   $225.95   $226.00  
  Purchase #4 $191.88   12.242%   $215.3699   $215.37   $215.35   $215.40  
  Purchase #5 $52.59   6.301%   $55.9037   $55.90   $55.90   $55.90  
  Purchase #6 $54.70   7.775%   $58.9529   $58.95   $58.95   $59.00  
  Purchase #7 $37.44   4.239%   $39.0271   $39.03   $39.05   $39.00  
  7 purchase totals = $981.22       $1,071.5100   $1,071.51   $1,071.50   $1,071.60