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 $46.84   11.337%   $52.1503   $52.15   $52.15   $52.20  
  Purchase #2 $216.82   13.351%   $245.7676   $245.77   $245.75   $245.80  
  Purchase #3 $243.99   4.329%   $254.5523   $254.55   $254.55   $254.60  
  Purchase #4 $123.73   3.241%   $127.7401   $127.74   $127.75   $127.70  
  Purchase #5 $64.97   3.647%   $67.3395   $67.34   $67.35   $67.30  
  Purchase #6 $217.25   9.412%   $237.6976   $237.70   $237.70   $237.70  
  Purchase #7 $219.31   11.589%   $244.7258   $244.73   $244.75   $244.70  
  7 purchase totals = $1,132.91       $1,229.9732   $1,229.98   $1,230.00   $1,230.00