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 $30.62   11.823%   $34.2402   $34.24   $34.25   $34.20  
  Purchase #2 $169.81   5.623%   $179.3584   $179.36   $179.35   $179.40  
  Purchase #3 $148.53   10.831%   $164.6173   $164.62   $164.60   $164.60  
  Purchase #4 $118.86   9.768%   $130.4702   $130.47   $130.45   $130.50  
  Purchase #5 $80.57   8.593%   $87.4934   $87.49   $87.50   $87.50  
  Purchase #6 $162.25   13.669%   $184.428   $184.43   $184.45   $184.40  
  Purchase #7 $207.81   10.112%   $228.8237   $228.82   $228.80   $228.80  
  7 purchase totals = $918.45       $1,009.4312   $1,009.43   $1,009.40   $1,009.40