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 $175.72   10.543%   $194.2462   $194.25   $194.25   $194.20  
  Purchase #2 $164.49   12.269%   $184.6713   $184.67   $184.65   $184.70  
  Purchase #3 $120.34   12.129%   $134.936   $134.94   $134.95   $134.90  
  Purchase #4 $57.98   9.590%   $63.5403   $63.54   $63.55   $63.50  
  Purchase #5 $174.37   10.624%   $192.8951   $192.90   $192.90   $192.90  
  Purchase #6 $89.69   13.589%   $101.878   $101.88   $101.90   $101.90  
  Purchase #7 $138.34   6.607%   $147.4801   $147.48   $147.50   $147.50  
  7 purchase totals = $920.93       $1,019.6470   $1,019.66   $1,019.70   $1,019.60