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 $92.32   3.465%   $95.5189   $95.52   $95.50   $95.50  
  Purchase #2 $34.41   7.277%   $36.914   $36.91   $36.90   $36.90  
  Purchase #3 $34.64   8.680%   $37.6468   $37.65   $37.65   $37.60  
  Purchase #4 $169.67   8.411%   $183.9409   $183.94   $183.95   $183.90  
  Purchase #5 $116.36   7.466%   $125.0474   $125.05   $125.05   $125.00  
  Purchase #6 $189.67   8.527%   $205.8432   $205.84   $205.85   $205.80  
  Purchase #7 $164.65   4.558%   $172.1547   $172.15   $172.15   $172.20  
  7 purchase totals = $801.72       $857.0659   $857.06   $857.05   $856.90