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 $132.77   3.525%   $137.4501   $137.45   $137.45   $137.50  
  Purchase #2 $120.36   7.283%   $129.1258   $129.13   $129.15   $129.10  
  Purchase #3 $212.96   12.135%   $238.8027   $238.80   $238.80   $238.80  
  Purchase #4 $92.76   13.637%   $105.4097   $105.41   $105.40   $105.40  
  Purchase #5 $106.56   9.870%   $117.0775   $117.08   $117.10   $117.10  
  Purchase #6 $107.93   12.209%   $121.1072   $121.11   $121.10   $121.10  
  Purchase #7 $228.81   3.172%   $236.0679   $236.07   $236.05   $236.10  
  7 purchase totals = $1,002.15       $1,085.0409   $1,085.05   $1,085.05   $1,085.10