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 $134.99   12.761%   $152.2161   $152.22   $152.20   $152.20  
  Purchase #2 $50.88   6.816%   $54.348   $54.35   $54.35   $54.30  
  Purchase #3 $193.61   7.731%   $208.578   $208.58   $208.60   $208.60  
  Purchase #4 $8.65   13.563%   $9.8232   $9.82   $9.80   $9.80  
  Purchase #5 $53.44   5.678%   $56.4743   $56.47   $56.45   $56.50  
  Purchase #6 $234.84   3.371%   $242.7565   $242.76   $242.75   $242.80  
  Purchase #7 $20.48   8.272%   $22.1741   $22.17   $22.15   $22.20  
  7 purchase totals = $696.89       $746.3702   $746.37   $746.30   $746.40