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 $88.54   9.213%   $96.6972   $96.70   $96.70   $96.70  
  Purchase #2 $233.66   3.848%   $242.6512   $242.65   $242.65   $242.70  
  Purchase #3 $31.89   8.250%   $34.5209   $34.52   $34.50   $34.50  
  Purchase #4 $158.84   6.472%   $169.1201   $169.12   $169.10   $169.10  
  Purchase #5 $84.69   3.155%   $87.362   $87.36   $87.35   $87.40  
  Purchase #6 $113.63   11.305%   $126.4759   $126.48   $126.50   $126.50  
  Purchase #7 $57.66   9.695%   $63.2501   $63.25   $63.25   $63.30  
  7 purchase totals = $768.91       $820.0774   $820.08   $820.05   $820.20