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 $204.86   11.709%   $228.8471   $228.85   $228.85   $228.80  
  Purchase #2 $129.47   3.864%   $134.4727   $134.47   $134.45   $134.50  
  Purchase #3 $226.52   10.106%   $249.4121   $249.41   $249.40   $249.40  
  Purchase #4 $73.90   3.655%   $76.601   $76.60   $76.60   $76.60  
  Purchase #5 $212.82   5.809%   $225.1827   $225.18   $225.20   $225.20  
  Purchase #6 $98.70   7.597%   $106.1982   $106.20   $106.20   $106.20  
  Purchase #7 $26.97   7.667%   $29.0378   $29.04   $29.05   $29.00  
  7 purchase totals = $973.24       $1,049.7516   $1,049.75   $1,049.75   $1,049.70