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 $165.49   12.242%   $185.7493   $185.75   $185.75   $185.70  
  Purchase #2 $169.77   7.713%   $182.8644   $182.86   $182.85   $182.90  
  Purchase #3 $133.45   6.789%   $142.5099   $142.51   $142.50   $142.50  
  Purchase #4 $15.48   7.130%   $16.5837   $16.58   $16.60   $16.60  
  Purchase #5 $68.67   13.869%   $78.1938   $78.19   $78.20   $78.20  
  Purchase #6 $186.50   8.126%   $201.655   $201.66   $201.65   $201.70  
  Purchase #7 $193.56   13.244%   $219.1951   $219.20   $219.20   $219.20  
  7 purchase totals = $932.92       $1,026.7512   $1,026.75   $1,026.75   $1,026.80