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 $249.91   10.473%   $276.0831   $276.08   $276.10   $276.10  
  Purchase #2 $140.28   8.133%   $151.689   $151.69   $151.70   $151.70  
  Purchase #3 $227.59   7.213%   $244.0061   $244.01   $244.00   $244.00  
  Purchase #4 $189.59   6.393%   $201.7105   $201.71   $201.70   $201.70  
  Purchase #5 $218.55   6.545%   $232.8541   $232.85   $232.85   $232.90  
  Purchase #6 $136.88   7.404%   $147.0146   $147.01   $147.00   $147.00  
  Purchase #7 $218.91   3.133%   $225.7685   $225.77   $225.75   $225.80  
  7 purchase totals = $1,381.71       $1,479.1259   $1,479.12   $1,479.10   $1,479.20