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 $120.96   4.821%   $126.7915   $126.79   $126.80   $126.80  
  Purchase #2 $180.75   6.470%   $192.4445   $192.44   $192.45   $192.40  
  Purchase #3 $148.67   13.447%   $168.6617   $168.66   $168.65   $168.70  
  Purchase #4 $133.44   8.850%   $145.2494   $145.25   $145.25   $145.20  
  Purchase #5 $145.93   3.769%   $151.4301   $151.43   $151.45   $151.40  
  Purchase #6 $193.46   11.593%   $215.8878   $215.89   $215.90   $215.90  
  Purchase #7 $73.87   4.782%   $77.4025   $77.40   $77.40   $77.40  
  7 purchase totals = $997.08       $1,077.8675   $1,077.86   $1,077.90   $1,077.80