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 $188.33   7.856%   $203.1252   $203.13   $203.15   $203.10  
  Purchase #2 $223.25   8.250%   $241.6681   $241.67   $241.65   $241.70  
  Purchase #3 $21.28   13.477%   $24.1479   $24.15   $24.15   $24.10  
  Purchase #4 $120.31   13.282%   $136.2896   $136.29   $136.30   $136.30  
  Purchase #5 $178.92   3.438%   $185.0713   $185.07   $185.05   $185.10  
  Purchase #6 $119.92   12.848%   $135.3273   $135.33   $135.35   $135.30  
  Purchase #7 $228.93   3.416%   $236.7502   $236.75   $236.75   $236.80  
  7 purchase totals = $1,080.94       $1,162.3796   $1,162.39   $1,162.40   $1,162.40