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 $186.34   11.111%   $207.0442   $207.04   $207.05   $207.00  
  Purchase #2 $219.41   6.480%   $233.6278   $233.63   $233.65   $233.60  
  Purchase #3 $87.71   6.728%   $93.6111   $93.61   $93.60   $93.60  
  Purchase #4 $201.45   5.367%   $212.2618   $212.26   $212.25   $212.30  
  Purchase #5 $176.93   5.219%   $186.164   $186.16   $186.15   $186.20  
  Purchase #6 $120.41   4.331%   $125.625   $125.63   $125.65   $125.60  
  Purchase #7 $206.77   11.159%   $229.8435   $229.84   $229.85   $229.80  
  7 purchase totals = $1,199.02       $1,288.1774   $1,288.17   $1,288.20   $1,288.10