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 $176.87   4.136%   $184.1853   $184.19   $184.20   $184.20  
  Purchase #2 $215.51   13.336%   $244.2504   $244.25   $244.25   $244.30  
  Purchase #3 $92.83   11.644%   $103.6391   $103.64   $103.65   $103.60  
  Purchase #4 $64.97   3.693%   $67.3693   $67.37   $67.35   $67.40  
  Purchase #5 $241.43   13.178%   $273.2456   $273.25   $273.25   $273.20  
  Purchase #6 $5.59   4.429%   $5.8376   $5.84   $5.85   $5.80  
  Purchase #7 $61.67   4.110%   $64.2046   $64.20   $64.20   $64.20  
  7 purchase totals = $858.87       $942.7319   $942.74   $942.75   $942.70