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 $22.93   11.868%   $25.6513   $25.65   $25.65   $25.70  
  Purchase #2 $178.76   13.515%   $202.9194   $202.92   $202.90   $202.90  
  Purchase #3 $60.40   5.502%   $63.7232   $63.72   $63.70   $63.70  
  Purchase #4 $132.32   13.795%   $150.5735   $150.57   $150.55   $150.60  
  Purchase #5 $228.71   5.771%   $241.9089   $241.91   $241.90   $241.90  
  Purchase #6 $233.64   7.650%   $251.5135   $251.51   $251.50   $251.50  
  Purchase #7 $74.91   9.651%   $82.1396   $82.14   $82.15   $82.10  
  7 purchase totals = $931.67       $1,018.4294   $1,018.42   $1,018.35   $1,018.40