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 $219.78   9.798%   $241.314   $241.31   $241.30   $241.30  
  Purchase #2 $118.35   4.301%   $123.4402   $123.44   $123.45   $123.40  
  Purchase #3 $161.77   9.565%   $177.2433   $177.24   $177.25   $177.20  
  Purchase #4 $204.30   10.257%   $225.2551   $225.26   $225.25   $225.30  
  Purchase #5 $134.30   8.660%   $145.9304   $145.93   $145.95   $145.90  
  Purchase #6 $92.92   12.282%   $104.3324   $104.33   $104.35   $104.30  
  Purchase #7 $64.92   5.177%   $68.2809   $68.28   $68.30   $68.30  
  7 purchase totals = $996.34       $1,085.7963   $1,085.79   $1,085.85   $1,085.70