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 $83.35   12.319%   $93.6179   $93.62   $93.60   $93.60  
  Purchase #2 $46.91   4.769%   $49.1471   $49.15   $49.15   $49.10  
  Purchase #3 $87.46   5.161%   $91.9738   $91.97   $91.95   $92.00  
  Purchase #4 $149.26   4.656%   $156.2095   $156.21   $156.20   $156.20  
  Purchase #5 $207.28   6.226%   $220.1853   $220.19   $220.20   $220.20  
  Purchase #6 $119.28   7.594%   $128.3381   $128.34   $128.35   $128.30  
  Purchase #7 $196.76   7.361%   $211.2435   $211.24   $211.25   $211.20  
  7 purchase totals = $890.30       $950.7152   $950.72   $950.70   $950.60