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 $94.69   9.505%   $103.6903   $103.69   $103.70   $103.70  
  Purchase #2 $89.37   5.398%   $94.1942   $94.19   $94.20   $94.20  
  Purchase #3 $30.42   5.332%   $32.042   $32.04   $32.05   $32.00  
  Purchase #4 $96.42   6.496%   $102.6834   $102.68   $102.70   $102.70  
  Purchase #5 $92.78   7.294%   $99.5474   $99.55   $99.55   $99.50  
  Purchase #6 $167.82   6.421%   $178.5957   $178.60   $178.60   $178.60  
  Purchase #7 $162.74   11.326%   $181.1719   $181.17   $181.15   $181.20  
  7 purchase totals = $734.24       $791.9249   $791.92   $791.95   $791.90