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 $57.77   6.301%   $61.4101   $61.41   $61.40   $61.40  
  Purchase #2 $123.43   8.704%   $134.1733   $134.17   $134.15   $134.20  
  Purchase #3 $246.74   8.843%   $268.5592   $268.56   $268.55   $268.60  
  Purchase #4 $122.95   9.777%   $134.9708   $134.97   $134.95   $135.00  
  Purchase #5 $162.45   9.606%   $178.0549   $178.05   $178.05   $178.10  
  Purchase #6 $180.41   10.596%   $199.5262   $199.53   $199.55   $199.50  
  Purchase #7 $34.49   6.556%   $36.7512   $36.75   $36.75   $36.80  
  7 purchase totals = $928.24       $1,013.4457   $1,013.44   $1,013.40   $1,013.60