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 $238.43   11.347%   $265.4847   $265.48   $265.50   $265.50  
  Purchase #2 $44.37   9.615%   $48.6362   $48.64   $48.65   $48.60  
  Purchase #3 $92.78   10.644%   $102.6555   $102.66   $102.65   $102.70  
  Purchase #4 $230.76   7.346%   $247.7116   $247.71   $247.70   $247.70  
  Purchase #5 $193.93   4.856%   $203.3472   $203.35   $203.35   $203.30  
  Purchase #6 $128.81   4.135%   $134.1363   $134.14   $134.15   $134.10  
  Purchase #7 $131.46   10.462%   $145.2133   $145.21   $145.20   $145.20  
  7 purchase totals = $1,060.54       $1,147.1848   $1,147.19   $1,147.20   $1,147.10