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 $160.66   9.276%   $175.5628   $175.56   $175.55   $175.60  
  Purchase #2 $222.82   5.792%   $235.7257   $235.73   $235.75   $235.70  
  Purchase #3 $27.49   12.449%   $30.9122   $30.91   $30.90   $30.90  
  Purchase #4 $152.82   9.808%   $167.8086   $167.81   $167.80   $167.80  
  Purchase #5 $169.45   5.568%   $178.885   $178.89   $178.90   $178.90  
  Purchase #6 $184.94   5.394%   $194.9157   $194.92   $194.90   $194.90  
  Purchase #7 $36.69   3.873%   $38.111   $38.11   $38.10   $38.10  
  7 purchase totals = $954.87       $1,021.9210   $1,021.93   $1,021.90   $1,021.90