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 $240.86   11.562%   $268.7082   $268.71   $268.70   $268.70  
  Purchase #2 $51.34   12.371%   $57.6913   $57.69   $57.70   $57.70  
  Purchase #3 $40.41   7.832%   $43.5749   $43.57   $43.55   $43.60  
  Purchase #4 $202.42   8.691%   $220.0123   $220.01   $220.00   $220.00  
  Purchase #5 $80.73   8.365%   $87.4831   $87.48   $87.50   $87.50  
  Purchase #6 $99.30   5.287%   $104.55   $104.55   $104.55   $104.60  
  Purchase #7 $211.93   9.238%   $231.5081   $231.51   $231.50   $231.50  
  7 purchase totals = $926.99       $1,013.5279   $1,013.52   $1,013.50   $1,013.60