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 $216.69   11.232%   $241.0286   $241.03   $241.05   $241.00  
  Purchase #2 $65.25   5.497%   $68.8368   $68.84   $68.85   $68.80  
  Purchase #3 $113.56   8.726%   $123.4692   $123.47   $123.45   $123.50  
  Purchase #4 $218.96   12.230%   $245.7388   $245.74   $245.75   $245.70  
  Purchase #5 $216.65   11.839%   $242.2992   $242.30   $242.30   $242.30  
  Purchase #6 $95.40   11.603%   $106.4693   $106.47   $106.45   $106.50  
  Purchase #7 $23.71   3.591%   $24.5614   $24.56   $24.55   $24.60  
  7 purchase totals = $950.22       $1,052.4033   $1,052.41   $1,052.40   $1,052.40