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 $176.73   11.750%   $197.4958   $197.50   $197.50   $197.50  
  Purchase #2 $168.29   3.372%   $173.9647   $173.96   $173.95   $174.00  
  Purchase #3 $27.75   7.550%   $29.8451   $29.85   $29.85   $29.80  
  Purchase #4 $180.73   3.394%   $186.864   $186.86   $186.85   $186.90  
  Purchase #5 $162.68   10.332%   $179.4881   $179.49   $179.50   $179.50  
  Purchase #6 $73.77   12.495%   $82.9876   $82.99   $83.00   $83.00  
  Purchase #7 $205.82   4.868%   $215.8393   $215.84   $215.85   $215.80  
  7 purchase totals = $995.77       $1,066.4846   $1,066.49   $1,066.50   $1,066.50