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 $56.88   10.799%   $63.0225   $63.02   $63.00   $63.00  
  Purchase #2 $152.59   6.718%   $162.841   $162.84   $162.85   $162.80  
  Purchase #3 $16.83   5.695%   $17.7885   $17.79   $17.80   $17.80  
  Purchase #4 $225.96   5.764%   $238.9843   $238.98   $239.00   $239.00  
  Purchase #5 $122.79   6.269%   $130.4877   $130.49   $130.50   $130.50  
  Purchase #6 $31.67   4.802%   $33.1908   $33.19   $33.20   $33.20  
  Purchase #7 $171.70   8.794%   $186.7993   $186.80   $186.80   $186.80  
  7 purchase totals = $778.42       $833.1141   $833.11   $833.15   $833.10