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 $64.98   5.510%   $68.5604   $68.56   $68.55   $68.60  
  Purchase #2 $188.61   5.574%   $199.1231   $199.12   $199.10   $199.10  
  Purchase #3 $225.92   11.214%   $251.2547   $251.25   $251.25   $251.30  
  Purchase #4 $88.31   12.671%   $99.4998   $99.50   $99.50   $99.50  
  Purchase #5 $54.80   5.712%   $57.9302   $57.93   $57.95   $57.90  
  Purchase #6 $250.27   5.495%   $264.0223   $264.02   $264.00   $264.00  
  Purchase #7 $52.27   5.417%   $55.1015   $55.10   $55.10   $55.10  
  7 purchase totals = $925.16       $995.4920   $995.48   $995.45   $995.50