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 $240.91   13.363%   $273.1028   $273.10   $273.10   $273.10  
  Purchase #2 $196.47   13.326%   $222.6516   $222.65   $222.65   $222.70  
  Purchase #3 $98.96   3.656%   $102.578   $102.58   $102.60   $102.60  
  Purchase #4 $66.86   5.567%   $70.5821   $70.58   $70.60   $70.60  
  Purchase #5 $247.63   12.492%   $278.5639   $278.56   $278.55   $278.60  
  Purchase #6 $177.29   9.795%   $194.6556   $194.66   $194.65   $194.70  
  Purchase #7 $148.32   8.439%   $160.8367   $160.84   $160.85   $160.80  
  7 purchase totals = $1,176.44       $1,302.9707   $1,302.97   $1,303.00   $1,303.10