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 $162.82   13.435%   $184.6949   $184.69   $184.70   $184.70  
  Purchase #2 $212.93   3.283%   $219.9205   $219.92   $219.90   $219.90  
  Purchase #3 $94.43   4.541%   $98.7181   $98.72   $98.70   $98.70  
  Purchase #4 $152.31   7.774%   $164.1506   $164.15   $164.15   $164.20  
  Purchase #5 $227.36   11.519%   $253.5496   $253.55   $253.55   $253.50  
  Purchase #6 $242.36   4.456%   $253.1596   $253.16   $253.15   $253.20  
  Purchase #7 $65.63   9.700%   $71.9961   $72.00   $72.00   $72.00  
  7 purchase totals = $1,157.84       $1,246.1894   $1,246.19   $1,246.15   $1,246.20