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 $46.90   9.785%   $51.4892   $51.49   $51.50   $51.50  
  Purchase #2 $206.74   7.363%   $221.9623   $221.96   $221.95   $222.00  
  Purchase #3 $139.62   10.135%   $153.7705   $153.77   $153.75   $153.80  
  Purchase #4 $232.74   13.219%   $263.5059   $263.51   $263.50   $263.50  
  Purchase #5 $206.64   5.302%   $217.5961   $217.60   $217.60   $217.60  
  Purchase #6 $68.42   5.162%   $71.9518   $71.95   $71.95   $72.00  
  Purchase #7 $172.79   11.682%   $192.9753   $192.98   $193.00   $193.00  
  7 purchase totals = $1,073.85       $1,173.2511   $1,173.26   $1,173.25   $1,173.40