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 $205.73   9.868%   $226.0314   $226.03   $226.05   $226.00  
  Purchase #2 $88.56   8.496%   $96.0841   $96.08   $96.10   $96.10  
  Purchase #3 $169.87   3.465%   $175.756   $175.76   $175.75   $175.80  
  Purchase #4 $31.81   8.190%   $34.4152   $34.42   $34.40   $34.40  
  Purchase #5 $65.29   7.649%   $70.284   $70.28   $70.30   $70.30  
  Purchase #6 $109.74   9.825%   $120.522   $120.52   $120.50   $120.50  
  Purchase #7 $32.76   11.736%   $36.6047   $36.60   $36.60   $36.60  
  7 purchase totals = $703.76       $759.6974   $759.69   $759.70   $759.70