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 $63.69   12.464%   $71.6283   $71.63   $71.65   $71.60  
  Purchase #2 $218.98   11.707%   $244.616   $244.62   $244.60   $244.60  
  Purchase #3 $86.49   6.151%   $91.81   $91.81   $91.80   $91.80  
  Purchase #4 $159.72   6.440%   $170.006   $170.01   $170.00   $170.00  
  Purchase #5 $223.84   11.548%   $249.689   $249.69   $249.70   $249.70  
  Purchase #6 $82.77   12.455%   $93.079   $93.08   $93.10   $93.10  
  Purchase #7 $246.54   3.840%   $256.0071   $256.01   $256.00   $256.00  
  7 purchase totals = $1,082.03       $1,176.8354   $1,176.85   $1,176.85   $1,176.80