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 $96.53   5.413%   $101.7552   $101.76   $101.75   $101.80  
  Purchase #2 $114.42   9.492%   $125.2807   $125.28   $125.30   $125.30  
  Purchase #3 $207.84   10.124%   $228.8817   $228.88   $228.90   $228.90  
  Purchase #4 $136.92   8.585%   $148.6746   $148.67   $148.65   $148.70  
  Purchase #5 $100.82   8.163%   $109.0499   $109.05   $109.05   $109.00  
  Purchase #6 $98.40   6.621%   $104.9151   $104.92   $104.90   $104.90  
  Purchase #7 $181.70   5.850%   $192.3295   $192.33   $192.35   $192.30  
  7 purchase totals = $936.63       $1,010.8867   $1,010.89   $1,010.90   $1,010.90