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 $194.46   11.441%   $216.7082   $216.71   $216.70   $216.70  
  Purchase #2 $37.65   5.194%   $39.6055   $39.61   $39.60   $39.60  
  Purchase #3 $247.62   8.556%   $268.8064   $268.81   $268.80   $268.80  
  Purchase #4 $232.25   11.741%   $259.5185   $259.52   $259.50   $259.50  
  Purchase #5 $145.59   3.637%   $150.8851   $150.89   $150.90   $150.90  
  Purchase #6 $118.63   6.284%   $126.0847   $126.08   $126.10   $126.10  
  Purchase #7 $55.66   5.769%   $58.871   $58.87   $58.85   $58.90  
  7 purchase totals = $1,031.86       $1,120.4794   $1,120.49   $1,120.45   $1,120.50