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 $141.72   13.440%   $160.7672   $160.77   $160.75   $160.80  
  Purchase #2 $172.74   6.363%   $183.7314   $183.73   $183.75   $183.70  
  Purchase #3 $53.90   7.125%   $57.7404   $57.74   $57.75   $57.70  
  Purchase #4 $228.67   8.366%   $247.8005   $247.80   $247.80   $247.80  
  Purchase #5 $57.63   7.583%   $62.0001   $62.00   $62.00   $62.00  
  Purchase #6 $188.66   4.690%   $197.5082   $197.51   $197.50   $197.50  
  Purchase #7 $130.39   12.586%   $146.8009   $146.80   $146.80   $146.80  
  7 purchase totals = $973.71       $1,056.3487   $1,056.35   $1,056.35   $1,056.30