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 $104.53   11.803%   $116.8677   $116.87   $116.85   $116.90  
  Purchase #2 $98.84   6.859%   $105.6194   $105.62   $105.60   $105.60  
  Purchase #3 $189.71   7.440%   $203.8244   $203.82   $203.80   $203.80  
  Purchase #4 $184.48   5.418%   $194.4751   $194.48   $194.50   $194.50  
  Purchase #5 $200.68   5.465%   $211.6472   $211.65   $211.65   $211.60  
  Purchase #6 $91.76   10.610%   $101.4957   $101.50   $101.50   $101.50  
  Purchase #7 $60.53   9.592%   $66.336   $66.34   $66.35   $66.30  
  7 purchase totals = $930.53       $1,000.2655   $1,000.28   $1,000.25   $1,000.20