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 $69.47   6.249%   $73.8112   $73.81   $73.80   $73.80  
  Purchase #2 $246.52   5.321%   $259.6373   $259.64   $259.65   $259.60  
  Purchase #3 $88.42   5.225%   $93.0399   $93.04   $93.05   $93.00  
  Purchase #4 $6.27   7.525%   $6.7418   $6.74   $6.75   $6.70  
  Purchase #5 $135.66   11.293%   $150.9801   $150.98   $151.00   $151.00  
  Purchase #6 $20.47   5.272%   $21.5492   $21.55   $21.55   $21.50  
  Purchase #7 $184.66   12.284%   $207.3436   $207.34   $207.35   $207.30  
  7 purchase totals = $751.47       $813.1031   $813.10   $813.15   $812.90