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 $24.53   9.710%   $26.9119   $26.91   $26.90   $26.90  
  Purchase #2 $194.69   5.325%   $205.0572   $205.06   $205.05   $205.10  
  Purchase #3 $221.86   11.297%   $246.9235   $246.92   $246.90   $246.90  
  Purchase #4 $114.76   7.866%   $123.787   $123.79   $123.80   $123.80  
  Purchase #5 $92.57   12.387%   $104.0366   $104.04   $104.05   $104.00  
  Purchase #6 $127.87   7.869%   $137.9321   $137.93   $137.95   $137.90  
  Purchase #7 $232.83   11.515%   $259.6404   $259.64   $259.65   $259.60  
  7 purchase totals = $1,009.11       $1,104.2887   $1,104.29   $1,104.30   $1,104.20