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 $157.47   7.430%   $169.17   $169.17   $169.15   $169.20  
  Purchase #2 $58.86   4.558%   $61.5428   $61.54   $61.55   $61.50  
  Purchase #3 $82.57   6.491%   $87.9296   $87.93   $87.95   $87.90  
  Purchase #4 $211.89   7.823%   $228.4662   $228.47   $228.45   $228.50  
  Purchase #5 $243.47   10.757%   $269.6601   $269.66   $269.65   $269.70  
  Purchase #6 $130.79   13.136%   $147.9706   $147.97   $147.95   $148.00  
  Purchase #7 $70.97   11.392%   $79.0549   $79.05   $79.05   $79.10  
  7 purchase totals = $956.02       $1,043.7942   $1,043.79   $1,043.75   $1,043.90