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 $93.97   10.769%   $104.0896   $104.09   $104.10   $104.10  
  Purchase #2 $195.87   12.162%   $219.6917   $219.69   $219.70   $219.70  
  Purchase #3 $233.47   4.204%   $243.2851   $243.29   $243.30   $243.30  
  Purchase #4 $207.33   10.180%   $228.4362   $228.44   $228.45   $228.40  
  Purchase #5 $179.33   12.459%   $201.6727   $201.67   $201.65   $201.70  
  Purchase #6 $23.85   5.830%   $25.2405   $25.24   $25.25   $25.20  
  Purchase #7 $220.81   12.535%   $248.4885   $248.49   $248.50   $248.50  
  7 purchase totals = $1,154.63       $1,270.9043   $1,270.91   $1,270.95   $1,270.90