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 $59.59   11.627%   $66.5185   $66.52   $66.50   $66.50  
  Purchase #2 $134.29   3.401%   $138.8572   $138.86   $138.85   $138.90  
  Purchase #3 $82.32   13.756%   $93.6439   $93.64   $93.65   $93.60  
  Purchase #4 $158.28   3.655%   $164.0651   $164.07   $164.05   $164.10  
  Purchase #5 $230.68   12.824%   $260.2624   $260.26   $260.25   $260.30  
  Purchase #6 $205.46   3.115%   $211.8601   $211.86   $211.85   $211.90  
  Purchase #7 $189.66   8.617%   $206.003   $206.00   $206.00   $206.00  
  7 purchase totals = $1,060.28       $1,141.2102   $1,141.21   $1,141.15   $1,141.30