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 $61.47   6.308%   $65.3475   $65.35   $65.35   $65.30  
  Purchase #2 $117.34   4.440%   $122.5499   $122.55   $122.55   $122.50  
  Purchase #3 $234.26   7.851%   $252.6518   $252.65   $252.65   $252.70  
  Purchase #4 $196.81   13.606%   $223.588   $223.59   $223.60   $223.60  
  Purchase #5 $67.42   8.589%   $73.2107   $73.21   $73.20   $73.20  
  Purchase #6 $105.49   6.703%   $112.561   $112.56   $112.55   $112.60  
  Purchase #7 $58.78   9.759%   $64.5163   $64.52   $64.50   $64.50  
  7 purchase totals = $841.57       $914.4252   $914.43   $914.40   $914.40