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 $200.67   13.609%   $227.9792   $227.98   $228.00   $228.00  
  Purchase #2 $161.72   10.595%   $178.8542   $178.85   $178.85   $178.90  
  Purchase #3 $142.57   3.219%   $147.1593   $147.16   $147.15   $147.20  
  Purchase #4 $233.92   12.171%   $262.3904   $262.39   $262.40   $262.40  
  Purchase #5 $229.25   11.136%   $254.7793   $254.78   $254.80   $254.80  
  Purchase #6 $10.53   5.385%   $11.097   $11.10   $11.10   $11.10  
  Purchase #7 $237.36   6.138%   $251.9292   $251.93   $251.95   $251.90  
  7 purchase totals = $1,216.02       $1,334.1886   $1,334.19   $1,334.25   $1,334.30