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 $6.96   4.777%   $7.2925   $7.29   $7.30   $7.30  
  Purchase #2 $194.48   6.250%   $206.635   $206.64   $206.65   $206.60  
  Purchase #3 $137.80   9.469%   $150.8483   $150.85   $150.85   $150.80  
  Purchase #4 $58.32   4.436%   $60.9071   $60.91   $60.90   $60.90  
  Purchase #5 $111.31   11.589%   $124.2097   $124.21   $124.20   $124.20  
  Purchase #6 $110.96   11.607%   $123.8391   $123.84   $123.85   $123.80  
  Purchase #7 $33.70   3.258%   $34.7979   $34.80   $34.80   $34.80  
  7 purchase totals = $653.53       $708.5296   $708.54   $708.55   $708.40