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 $88.66   9.353%   $96.9524   $96.95   $96.95   $97.00  
  Purchase #2 $72.57   10.512%   $80.1986   $80.20   $80.20   $80.20  
  Purchase #3 $228.75   8.681%   $248.6078   $248.61   $248.60   $248.60  
  Purchase #4 $121.85   7.339%   $130.7926   $130.79   $130.80   $130.80  
  Purchase #5 $223.82   13.750%   $254.5953   $254.60   $254.60   $254.60  
  Purchase #6 $53.84   5.815%   $56.9708   $56.97   $56.95   $57.00  
  Purchase #7 $121.75   12.166%   $136.5621   $136.56   $136.55   $136.60  
  7 purchase totals = $911.24       $1,004.6796   $1,004.68   $1,004.65   $1,004.80