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 $68.44   8.783%   $74.4511   $74.45   $74.45   $74.50  
  Purchase #2 $165.98   5.137%   $174.5064   $174.51   $174.50   $174.50  
  Purchase #3 $77.80   13.281%   $88.1326   $88.13   $88.15   $88.10  
  Purchase #4 $240.60   10.840%   $266.681   $266.68   $266.70   $266.70  
  Purchase #5 $235.49   13.634%   $267.5967   $267.60   $267.60   $267.60  
  Purchase #6 $169.46   10.765%   $187.7024   $187.70   $187.70   $187.70  
  Purchase #7 $7.62   6.622%   $8.1246   $8.12   $8.10   $8.10  
  7 purchase totals = $965.39       $1,067.1948   $1,067.19   $1,067.20   $1,067.20