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 $68.82   5.389%   $72.5287   $72.53   $72.55   $72.50  
  Purchase #2 $168.41   9.513%   $184.4308   $184.43   $184.45   $184.40  
  Purchase #3 $235.55   12.574%   $265.1681   $265.17   $265.15   $265.20  
  Purchase #4 $234.49   5.187%   $246.653   $246.65   $246.65   $246.70  
  Purchase #5 $176.62   10.684%   $195.4901   $195.49   $195.50   $195.50  
  Purchase #6 $10.56   11.321%   $11.7555   $11.76   $11.75   $11.80  
  Purchase #7 $79.51   13.431%   $90.189   $90.19   $90.20   $90.20  
  7 purchase totals = $973.96       $1,066.2152   $1,066.22   $1,066.25   $1,066.30