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 $42.71   9.618%   $46.8178   $46.82   $46.80   $46.80  
  Purchase #2 $227.39   8.169%   $245.9655   $245.97   $245.95   $246.00  
  Purchase #3 $128.35   13.418%   $145.572   $145.57   $145.55   $145.60  
  Purchase #4 $45.68   9.373%   $49.9616   $49.96   $49.95   $50.00  
  Purchase #5 $227.94   6.525%   $242.8131   $242.81   $242.80   $242.80  
  Purchase #6 $200.26   8.172%   $216.6252   $216.63   $216.65   $216.60  
  Purchase #7 $82.32   7.182%   $88.2322   $88.23   $88.25   $88.20  
  7 purchase totals = $954.65       $1,035.9874   $1,035.99   $1,035.95   $1,036.00