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 $58.56   8.688%   $63.6477   $63.65   $63.65   $63.60  
  Purchase #2 $209.60   11.164%   $232.9997   $233.00   $233.00   $233.00  
  Purchase #3 $62.66   3.150%   $64.6338   $64.63   $64.65   $64.60  
  Purchase #4 $225.63   3.705%   $233.9896   $233.99   $234.00   $234.00  
  Purchase #5 $8.98   8.319%   $9.727   $9.73   $9.75   $9.70  
  Purchase #6 $59.94   13.526%   $68.0475   $68.05   $68.05   $68.00  
  Purchase #7 $89.58   10.700%   $99.1651   $99.17   $99.15   $99.20  
  7 purchase totals = $714.95       $772.2104   $772.22   $772.25   $772.10