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 $109.42   8.819%   $119.0697   $119.07   $119.05   $119.10  
  Purchase #2 $149.98   8.155%   $162.2109   $162.21   $162.20   $162.20  
  Purchase #3 $67.82   5.783%   $71.742   $71.74   $71.75   $71.70  
  Purchase #4 $77.61   9.269%   $84.8037   $84.80   $84.80   $84.80  
  Purchase #5 $215.27   4.597%   $225.166   $225.17   $225.15   $225.20  
  Purchase #6 $228.48   8.457%   $247.8026   $247.80   $247.80   $247.80  
  Purchase #7 $146.39   9.622%   $160.4756   $160.48   $160.50   $160.50  
  7 purchase totals = $994.97       $1,071.2705   $1,071.27   $1,071.25   $1,071.30