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 $63.67   3.142%   $65.6705   $65.67   $65.65   $65.70  
  Purchase #2 $141.41   12.812%   $159.5274   $159.53   $159.55   $159.50  
  Purchase #3 $10.78   6.648%   $11.4967   $11.50   $11.50   $11.50  
  Purchase #4 $181.77   8.836%   $197.8312   $197.83   $197.85   $197.80  
  Purchase #5 $177.41   8.839%   $193.0913   $193.09   $193.10   $193.10  
  Purchase #6 $50.25   6.287%   $53.4092   $53.41   $53.40   $53.40  
  Purchase #7 $215.95   5.651%   $228.1533   $228.15   $228.15   $228.20  
  7 purchase totals = $841.24       $909.1796   $909.18   $909.20   $909.20