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 $235.67   13.515%   $267.5208   $267.52   $267.50   $267.50  
  Purchase #2 $23.48   10.761%   $26.0067   $26.01   $26.00   $26.00  
  Purchase #3 $223.42   8.639%   $242.7213   $242.72   $242.70   $242.70  
  Purchase #4 $174.59   4.602%   $182.6246   $182.62   $182.60   $182.60  
  Purchase #5 $49.59   6.242%   $52.6854   $52.69   $52.70   $52.70  
  Purchase #6 $28.73   10.138%   $31.6426   $31.64   $31.65   $31.60  
  Purchase #7 $231.95   5.817%   $245.4425   $245.44   $245.45   $245.40  
  7 purchase totals = $967.43       $1,048.6439   $1,048.64   $1,048.60   $1,048.50