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 $239.82   5.470%   $252.9382   $252.94   $252.95   $252.90  
  Purchase #2 $141.59   6.234%   $150.4167   $150.42   $150.40   $150.40  
  Purchase #3 $130.86   7.542%   $140.7295   $140.73   $140.75   $140.70  
  Purchase #4 $195.36   12.123%   $219.0435   $219.04   $219.05   $219.00  
  Purchase #5 $59.40   6.299%   $63.1416   $63.14   $63.15   $63.10  
  Purchase #6 $217.71   11.165%   $242.0173   $242.02   $242.00   $242.00  
  Purchase #7 $177.82   7.702%   $191.5157   $191.52   $191.50   $191.50  
  7 purchase totals = $1,162.56       $1,259.8025   $1,259.81   $1,259.80   $1,259.60