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 $71.58   8.525%   $77.6822   $77.68   $77.70   $77.70  
  Purchase #2 $189.41   4.170%   $197.3084   $197.31   $197.30   $197.30  
  Purchase #3 $95.86   3.873%   $99.5727   $99.57   $99.55   $99.60  
  Purchase #4 $129.54   8.815%   $140.959   $140.96   $140.95   $141.00  
  Purchase #5 $209.61   11.446%   $233.602   $233.60   $233.60   $233.60  
  Purchase #6 $231.94   11.172%   $257.8523   $257.85   $257.85   $257.90  
  Purchase #7 $20.60   7.828%   $22.2126   $22.21   $22.20   $22.20  
  7 purchase totals = $948.54       $1,029.1892   $1,029.18   $1,029.15   $1,029.30