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 $186.65   12.846%   $210.6271   $210.63   $210.65   $210.60  
  Purchase #2 $112.49   4.841%   $117.9356   $117.94   $117.95   $117.90  
  Purchase #3 $47.66   6.601%   $50.806   $50.81   $50.80   $50.80  
  Purchase #4 $211.29   10.692%   $233.8811   $233.88   $233.90   $233.90  
  Purchase #5 $18.58   3.317%   $19.1963   $19.20   $19.20   $19.20  
  Purchase #6 $201.70   11.109%   $224.1069   $224.11   $224.10   $224.10  
  Purchase #7 $138.87   8.621%   $150.842   $150.84   $150.85   $150.80  
  7 purchase totals = $917.24       $1,007.3950   $1,007.41   $1,007.45   $1,007.30