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 $243.49   10.708%   $269.5629   $269.56   $269.55   $269.60  
  Purchase #2 $21.97   10.597%   $24.2982   $24.30   $24.30   $24.30  
  Purchase #3 $57.44   11.488%   $64.0387   $64.04   $64.05   $64.00  
  Purchase #4 $142.87   5.697%   $151.0093   $151.01   $151.00   $151.00  
  Purchase #5 $60.96   6.217%   $64.7499   $64.75   $64.75   $64.70  
  Purchase #6 $116.33   12.304%   $130.6432   $130.64   $130.65   $130.60  
  Purchase #7 $190.51   4.213%   $198.5362   $198.54   $198.55   $198.50  
  7 purchase totals = $833.57       $902.8384   $902.84   $902.85   $902.70