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 $88.44   8.624%   $96.0671   $96.07   $96.05   $96.10  
  Purchase #2 $85.88   8.830%   $93.4632   $93.46   $93.45   $93.50  
  Purchase #3 $249.90   9.273%   $273.0732   $273.07   $273.05   $273.10  
  Purchase #4 $91.97   11.522%   $102.5668   $102.57   $102.55   $102.60  
  Purchase #5 $49.35   10.594%   $54.5781   $54.58   $54.60   $54.60  
  Purchase #6 $204.29   5.553%   $215.6342   $215.63   $215.65   $215.60  
  Purchase #7 $229.33   7.842%   $247.3141   $247.31   $247.30   $247.30  
  7 purchase totals = $999.16       $1,082.6967   $1,082.69   $1,082.65   $1,082.80