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 $63.28   9.483%   $69.2808   $69.28   $69.30   $69.30  
  Purchase #2 $183.46   10.697%   $203.0847   $203.08   $203.10   $203.10  
  Purchase #3 $250.35   9.385%   $273.8453   $273.85   $273.85   $273.80  
  Purchase #4 $203.62   4.697%   $213.184   $213.18   $213.20   $213.20  
  Purchase #5 $240.82   12.811%   $271.6715   $271.67   $271.65   $271.70  
  Purchase #6 $243.65   10.240%   $268.5998   $268.60   $268.60   $268.60  
  Purchase #7 $5.35   6.177%   $5.6805   $5.68   $5.70   $5.70  
  7 purchase totals = $1,190.53       $1,305.3466   $1,305.34   $1,305.40   $1,305.40