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 $74.74   6.520%   $79.613   $79.61   $79.60   $79.60  
  Purchase #2 $136.86   6.435%   $145.6669   $145.67   $145.65   $145.70  
  Purchase #3 $162.52   6.361%   $172.8579   $172.86   $172.85   $172.90  
  Purchase #4 $219.48   12.425%   $246.7504   $246.75   $246.75   $246.80  
  Purchase #5 $159.61   5.520%   $168.4205   $168.42   $168.40   $168.40  
  Purchase #6 $244.46   12.652%   $275.3891   $275.39   $275.40   $275.40  
  Purchase #7 $70.45   8.177%   $76.2107   $76.21   $76.20   $76.20  
  7 purchase totals = $1,068.12       $1,164.9085   $1,164.91   $1,164.85   $1,165.00