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 $197.96   3.223%   $204.3403   $204.34   $204.35   $204.30  
  Purchase #2 $243.73   9.383%   $266.5992   $266.60   $266.60   $266.60  
  Purchase #3 $49.44   12.454%   $55.5973   $55.60   $55.60   $55.60  
  Purchase #4 $193.64   3.183%   $199.8036   $199.80   $199.80   $199.80  
  Purchase #5 $125.53   8.356%   $136.0193   $136.02   $136.00   $136.00  
  Purchase #6 $143.90   12.616%   $162.0544   $162.05   $162.05   $162.10  
  Purchase #7 $23.53   8.765%   $25.5924   $25.59   $25.60   $25.60  
  7 purchase totals = $977.73       $1,050.0065   $1,050.00   $1,050.00   $1,050.00