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 $202.34   12.500%   $227.6325   $227.63   $227.65   $227.60  
  Purchase #2 $88.45   8.367%   $95.8506   $95.85   $95.85   $95.90  
  Purchase #3 $24.34   8.789%   $26.4792   $26.48   $26.50   $26.50  
  Purchase #4 $189.87   7.647%   $204.3894   $204.39   $204.40   $204.40  
  Purchase #5 $250.92   6.249%   $266.6   $266.60   $266.60   $266.60  
  Purchase #6 $160.63   3.852%   $166.8175   $166.82   $166.80   $166.80  
  Purchase #7 $218.31   6.268%   $231.9937   $231.99   $232.00   $232.00  
  7 purchase totals = $1,134.86       $1,219.7629   $1,219.76   $1,219.80   $1,219.80