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 $58.53   11.782%   $65.426   $65.43   $65.45   $65.40  
  Purchase #2 $215.93   11.548%   $240.8656   $240.87   $240.85   $240.90  
  Purchase #3 $116.78   7.494%   $125.5315   $125.53   $125.55   $125.50  
  Purchase #4 $223.49   9.573%   $244.8847   $244.88   $244.90   $244.90  
  Purchase #5 $66.97   4.531%   $70.0044   $70.00   $70.00   $70.00  
  Purchase #6 $109.70   11.355%   $122.1564   $122.16   $122.15   $122.20  
  Purchase #7 $218.63   5.531%   $230.7224   $230.72   $230.70   $230.70  
  7 purchase totals = $1,010.03       $1,099.5910   $1,099.59   $1,099.60   $1,099.60