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 $147.40   9.130%   $160.8576   $160.86   $160.85   $160.90  
  Purchase #2 $245.28   7.482%   $263.6318   $263.63   $263.65   $263.60  
  Purchase #3 $140.44   10.382%   $155.0205   $155.02   $155.00   $155.00  
  Purchase #4 $224.56   10.168%   $247.3933   $247.39   $247.40   $247.40  
  Purchase #5 $107.43   5.299%   $113.1227   $113.12   $113.10   $113.10  
  Purchase #6 $99.64   3.204%   $102.8325   $102.83   $102.85   $102.80  
  Purchase #7 $44.76   5.417%   $47.1846   $47.18   $47.20   $47.20  
  7 purchase totals = $1,009.51       $1,090.0430   $1,090.03   $1,090.05   $1,090.00