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 $90.82   12.629%   $102.2897   $102.29   $102.30   $102.30  
  Purchase #2 $164.27   8.608%   $178.4104   $178.41   $178.40   $178.40  
  Purchase #3 $30.43   8.227%   $32.9335   $32.93   $32.95   $32.90  
  Purchase #4 $211.28   10.331%   $233.1073   $233.11   $233.10   $233.10  
  Purchase #5 $34.41   4.651%   $36.0104   $36.01   $36.00   $36.00  
  Purchase #6 $214.54   5.543%   $226.432   $226.43   $226.45   $226.40  
  Purchase #7 $200.66   12.182%   $225.1044   $225.10   $225.10   $225.10  
  7 purchase totals = $946.41       $1,034.2877   $1,034.28   $1,034.30   $1,034.20