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 $88.72   3.744%   $92.0417   $92.04   $92.05   $92.00  
  Purchase #2 $155.39   6.406%   $165.3443   $165.34   $165.35   $165.30  
  Purchase #3 $58.53   3.466%   $60.5586   $60.56   $60.55   $60.60  
  Purchase #4 $194.42   11.813%   $217.3868   $217.39   $217.40   $217.40  
  Purchase #5 $15.31   3.547%   $15.853   $15.85   $15.85   $15.90  
  Purchase #6 $208.99   4.518%   $218.4322   $218.43   $218.45   $218.40  
  Purchase #7 $247.88   8.765%   $269.6067   $269.61   $269.60   $269.60  
  7 purchase totals = $969.24       $1,039.2233   $1,039.22   $1,039.25   $1,039.20