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 $62.36   10.419%   $68.8573   $68.86   $68.85   $68.90  
  Purchase #2 $223.99   12.336%   $251.6214   $251.62   $251.60   $251.60  
  Purchase #3 $230.46   5.726%   $243.6561   $243.66   $243.65   $243.70  
  Purchase #4 $144.37   9.295%   $157.7892   $157.79   $157.80   $157.80  
  Purchase #5 $173.68   7.238%   $186.251   $186.25   $186.25   $186.30  
  Purchase #6 $24.64   4.438%   $25.7335   $25.73   $25.75   $25.70  
  Purchase #7 $29.57   8.757%   $32.1594   $32.16   $32.15   $32.20  
  7 purchase totals = $889.07       $966.0679   $966.07   $966.05   $966.20