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 $164.89   8.768%   $179.3476   $179.35   $179.35   $179.30  
  Purchase #2 $95.88   9.422%   $104.9138   $104.91   $104.90   $104.90  
  Purchase #3 $176.77   9.457%   $193.4871   $193.49   $193.50   $193.50  
  Purchase #4 $200.37   7.107%   $214.6103   $214.61   $214.60   $214.60  
  Purchase #5 $62.79   12.764%   $70.8045   $70.80   $70.80   $70.80  
  Purchase #6 $7.32   3.799%   $7.5981   $7.60   $7.60   $7.60  
  Purchase #7 $166.85   3.281%   $172.3243   $172.32   $172.30   $172.30  
  7 purchase totals = $874.87       $943.0857   $943.08   $943.05   $943.00