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 $109.57   9.489%   $119.9671   $119.97   $119.95   $120.00  
  Purchase #2 $45.75   7.849%   $49.3409   $49.34   $49.35   $49.30  
  Purchase #3 $24.91   4.188%   $25.9532   $25.95   $25.95   $26.00  
  Purchase #4 $142.96   13.829%   $162.7299   $162.73   $162.75   $162.70  
  Purchase #5 $167.59   4.208%   $174.6422   $174.64   $174.65   $174.60  
  Purchase #6 $185.87   8.258%   $201.2191   $201.22   $201.20   $201.20  
  Purchase #7 $53.79   6.279%   $57.1675   $57.17   $57.15   $57.20  
  7 purchase totals = $730.44       $791.0199   $791.02   $791.00   $791.00